Respiratory therapy system including a nasal cannula assembly

ABSTRACT

A nasal cannula for supplying a respiratory gas to a patient and a method of treating a patient with sleep disorder. The nasal cannula comprises a pair of spaced apart supply lines which each have a head at one end thereof with a discharge opening located therein. The opposite end of each supply line is connectable to a high flow respiratory gas source. Each head is sized to be snugly received and retained within one of the nasal cavities of the patient while forming a sufficient leakage passage, between a portion of inwardly facing nasal cavity skin of a patient and a portion of an exterior surface of the head, to facilitate exhausting of any excess respiratory gas supplied to the patient through the leakage passage and also facilitate inhalation of any room air required in excess of the respiratory gas to be supplied to the patient.

This Application is a national stage completion of PCT/US2009/031824filed on Jan. 23, 2009 which is a continuation-in-part of provisionalapplication No. 61/023,571 filed Jan. 25, 2008.

FIELD OF THE INVENTION

The present invention relates in general to respiratory assistanceequipment and, in particular, to a respiratory therapy system includinga nasal cannula assembly for use in the administration of fluids such asoxygen into the nasal passages of a patient having respiratory ailments.

BACKGROUND OF THE INVENTION

A variety of flexible cannulas have been produced that are positioned tocontact the nasal-labial area between the patient's upper lip andnostrils. Even though many of these cannulas were made of soft, flexibleplastic, the wearer frequently encountered discomfort because a cannulais usually worn for a prolonged period of time. This results incontinued contact of the cannula with the wearer's facial tissues,especially at the philtrum and around the unprotected nasal-labial area,thereby causing irritation and inflammation.

The structures of conventional cannula devices may be categorized intotwo general groups.

The first group utilizes a unitary member that includes a main tubularportion and a pair of tubular nasal prongs integrally connected to andin fluid communication with the main tubular portion. The main tubularportion has opposite ends which are connectable to flexible auxiliaryoxygen supply tubes that are looped over the patient's ears and whichthemselves are in fluid communication with a pressurized source ofoxygen. As is known, the nasal prongs are inserted into the nares of thewearer to deliver a low flow of oxygen to the patient's respiratorytract. The main tubular portion of these devices spans much if not allof the length of a wearer's upper lip. In so doing, the main tubularportion exerts contact pressure across much of the patient's upper lip.Under these circumstances, a patient usually begins to experiencediscomfort in a relatively short period of time even if the cannulaitself and the auxiliary oxygen supply tubes connected thereto aredesigned to deliver relatively low flows of oxygen, i.e., they notparticularly robust, stiff or heavy in weight. Examples of cannuladevices and assemblies constructed in accordance with this first groupmay be found in, for example, U.S. Pat. Nos. 2,868,199; 3,643,660;3,802,431; 4,106,505; 4,156,426; 5,400,776 and 5,794,619 and inpublished U.S. Patent Application Publications Nos. U.S. 2001/0031929 A1and U.S. 2002/0112730 A1.

The second group involves a harness member that does not itself conveyoxygen but which retains flexible auxiliary oxygen supply tubes in sucha way that their discharge outlet ends define nasal prongs. However, theharness members of these devices also typically span all or most of thelength of a patent's upper lip whereby the devices, even for light-dutygas delivery applications, produce the same patient discomfort problemsas the cannula devices of the first group. Examples of cannula devicesconstructed according to the second group may be found in, for example,U.S. Pat. Nos. 2,931,358; 3,400,714; 4,278,082; 4,648,398; 4,790,308;4,818,320 and 5,533,506.

Published United States Patent Application Publication No. U.S.2002/0046755 A1 (the '755 publication) discloses various embodiments ofnasal cannulas that fall into one or the other of the aforementionedgroups, as well as other embodiments that are not as readilyclassifiable. However, none of the nasal cannulas disclosed in thatpublication describe a device that would be comfortable to a patientunder the high flow conditions a patient would experience under positiveairway pressure therapy, e.g., continuous positive airway pressure(CPAP) or bilevel positive airway pressure (BiPAP), that is oftenprescribed to patients suffering from Obstructive Sleep Apnea (OSA). Forexample, according to one embodiment of cannula taught in the '755publication, a relatively narrow connector member that would restagainst a patient's upper lip is integrally attached to the flexibleauxiliary oxygen supply tubes whereby the ends of the tubes wouldfunction as nasal prongs that elastically engage the user's nasal septuminside of the nostrils. As used herein, the term “nasal septum,” orsimply “septum,” means the wall that divides the nasal cavity intohalves which terminate at the nostrils. At its front or anterior portionthe septum is a firm but bendable structure made mostly of cartilagethat is covered by skin. In order to deliver respiratory gas flow to acannula that would be therapeutically desirable to maintain a typicaladult patient's respiratory passageways open during OSA, for example,conventional auxiliary oxygen supply tubes must have an outer diameterof up to about ¼ inch (0.635 cm). Tubes of this caliber, when insertedshort distances into the nostrils (as they must be so as not to harm theinternal nasal tissues), would be quite obtrusive, stiff anduncomfortable to the user, especially when in elastic contact with theuser's septum. Such discomfort would, in turn, detrimentally impact thepatient's compliance with his or her prescribed positive airway pressureregime and, therefore, reduce the overall effectiveness of therapy.

U.S. Pat. Nos. 4,782,832; 5,042,478; 5,134,995; 5,269,296; 5,535,739;5,687,715; 5,752,510; 6,431,172 and 6,478,026, as well as publishedUnited States Patent Application Publication No. U.S. 2002/005935 A1,described nasal cannulas for positive airway pressure therapy. However,the cannula devices disclosed in these documents are quite large andcumbersome. Indeed, many are designed to cover and/or seal the patient'snostrils. Consequently, they too are not conducive to optimum patienttherapy compliance.

An advantage exists, therefore, for respiratory therapy system includinga nasal cannula assembly that is compact, lightweight and fabricatedfrom highly flexible material. So constructed, the assembly would becomfortable for patients that undergo respiratory therapy involving theadministration of pressurized respiratory gases for extended periods oftime, including therapy involving the administration of pressurizedrespiratory gases at the high flow rates that are useful in positiveairway pressure therapy.

SUMMARY OF THE INVENTION

The present invention provides a respiratory therapy system including anasal cannula assembly adapted to contact the nasal-labial area of apatient's face. The cannula assembly comprises a nasal cannula, a pairof flexible auxiliary respiratory gas supply lines connected to thenasal cannula, a main respiratory gas supply line and, possibly a sliploop disposed about the auxiliary supply lines.

The nasal cannula is a unitary member desirably made of a highlyflexible or pliable material. The cannula is molded so as to define anarrow central member and a pair of flexible supply arms integrallyformed along opposite edges of the central member that are connectableto pair of auxiliary respiratory gas supply lines. The inner ends of thesupply arms define a pair of spaced-apart hollow tubular extensions orprongs projecting in a slightly curved configuration from the centralmember. The tubular extensions are inserted into the nostrils of thewearer and their slightly curved configuration permits a positiveguiding of the respiratory gas supply along the natural contours of thenasal passages into the pharynx.

The upper surface of the central member is preferably rounded in orderto minimize the area of contact on the lower, outer surface of the nasalseptum and to avoid any straight or sharp edges that would concentratepressure against the septum. This, coupled with the inherent flexibilityand short length of the central member, allows the cannula to lightlycontact a small portion of the nasal-labial area of the patient.

In addition, the flexible supply arms of the cannula are designed suchthat when they are connected to the auxiliary respiratory gas supplylines and the cannula assembly is properly donned by the patient, thearms flex in such a way as to urge the auxiliary respiratory gas supplylines to pass under, rather than across or above, the patient'scheekbones. The advantage of this effect is that it avoids thediscomfort that some patients experience when nasal cannula auxiliaryrespiratory gas supply lines contact the tissues of their cheekbonestructures. Thus, when the nasal cannula assembly of the presentinvention is subjected to the pulling force of the auxiliary respiratorygas supply lines when the assembly is worn by a patient, it exertsminimal pressure against the patient's nasal-labial. In addition, itprovides positive positioning of the tubular extensions within the nasalpassages while spacing their surfaces from the interior walls of thenasal passages, including the septum. The result is a highly comfortableassembly that can be worn by a patient for long periods of time evenunder conditions of high gas flow rate whereby the patient is morelikely to comply with and obtain the optimum benefits from his or herrespiratory therapy regime.

Another object of the present invention is to increase resistance to thepatient, upon exhalation, while not substantially increasing thebreathing work of the patient during inhalation so that the breathingrate of the patient remains substantially at the same rate.

Still another object of the present invention is to introduce asufficient amount of a treating or a respiratory gas, such as oxygen,medicine, etc. (all of which hereinafter are referred to as a“respiratory gas”) into the nasal cavity of the patient in order todilute or blow or drive off much of the carbon dioxide, in the processof being exhaled by the patient during an exhalation breath, and replacethat blown or driven off carbon dioxide with the respiratory gas whichcan thereafter be readily inhaled by the patient during his/hersubsequent inhalation breath.

Yet another object of the present invention is to provide a respiratorygas supply system which is readily retained within the nostrils of apatient while still being received therein so as to facilitate leakagebetween the inwardly facing nostril skin and the exterior surfaces ofthe nasal prongs to permit blowing or driving off some of the carbondioxide contained within the exhalation breath of the patient.

A still further object of the present invention is to normally providean excess quantity of the respiratory gas to the patient, at a variableflow rate, while allowing some of the excess respiratory gas to leakbetween the inwardly facing nostril skin and the exterior surfaces ofthe nasal prongs.

Another object of the present invention is to design a respiratory gassupply system which adequately heats and moisturizes the respiratorygas, prior to delivering the same to the patient, while also minimizingany condensation, along the supply conduit, of moisture contained in therespiratory gas and also reducing the noise generated by the respiratorygas supply system, to a decibel level approaching about 46 decibel,during delivery of the respiratory gas.

A further object of the present invention is to generate and maintain asufficient back pressure in the patient, utilizing the respiratory gassupply system, so that the soft palate of the patient remainsufficiently inflated and is prevented from collapsing.

Still another object of the present invention is to provide arespiratory gas supply system which is able to treat sleep apnea.

A further object of the invention is to modulate or vary the flow rateof the gas supply source such that the gas supply source normallymaintains a gas supply pressure of about 8 centimeters of water or sowhile the gas supply pressure may drop to about 6 centimeters of wateror so, during inhalation by the patient, and may increase to about 10centimeters of water or so, during exhalation by the patient. Duringpatient exhalation, the supplied excess gas leaks out, between the headsof the nasal cannula and the skin of the nostrils of the patient, andoperation of the gas supply source may slow down, or possiblytemporarily discontinue for a short duration of time, in an effort tomaintain the gas supply pressure of about 8 centimeters of water or so.

Still another object of the invention is to provide a gas supply nasalcannula breathing system which closely tracks the breathing functions ofthe patient to ensure that the patient receives an ample supply of gasand the patient does not experience or perceive that he/she is“starving” for the supply gas, e.g., air, during use of the gas supplynasal cannula breathing system.

Another object of the invention is to develop a relatively high pressuredrop, e.g., about 22 mm Hg, in the gas supply nasal cannula breathingsystem, between the gas supply source and the nasal cannula, and providea gas supply nasal cannula breathing system which can fairly accuratelypredict the breathing characteristics being currently experienced by thepatient.

The present invention relates to a nasal cannula for supplying arespiratory gas to a patient, the nasal cannula comprising: a pair ofsupply lines which each have a head at one end thereof with a dischargeopening therein for discharging a respiratory gas, and the opposite endof each of the pair of supply lines being connectable to a respiratorygas source; wherein each head is sized to be snugly received andretained within one of the nasal cavities of the patient while forming asufficient leakage passage, between a portion of inwardly facing nasalcavity skin of a patient and a portion of an exterior surface of thehead, to facilitate exhausting of any excess respiratory gas supplied tothe patient through the leakage passage and also facilitate inhalationof any room air required in excess of the respiratory gas to be suppliedto the patient.

The present invention relates to a nasal cannula assembly for supplyinga respiratory gas to a patient, the nasal cannula assembly comprising: apair of supply lines which each have a head at one end thereof with adischarge opening therein for discharging a respiratory gas, and theopposite end of each of the pair of supply lines being connected to anauxiliary respiratory gas supply line; and a remote end of each of theauxiliary respiratory gas supply line is connected with a respiratorygas source for supplying a respiratory gas to a patient; wherein eachhead is sized to be snugly received and retained within one of the nasalcavities of the patient while forming a sufficient leakage passage,between a portion of inwardly facing nasal cavity skin of a patient anda portion of an exterior surface of the head, to facilitate exhaustingof excess respiratory gas supplied to the patient through the leakagepassage.

The present invention relates to a respiratory therapy system forsupplying a respiratory gas to a patient via a nasal cannula, therespiratory therapy system comprising: a source of respiratory gas forsupplying a respiratory gas to a patient; a nasal cannula connected tothe source of respiratory gas for receiving the respiratory gas andsupplying the respiratory gas to nostrils of a patient; the nasalcannula comprising: a pair of supply lines which each have a head at oneend thereof with a discharge opening therein for discharging arespiratory gas, and the opposite end of each of the pair of supplylines being connected to an auxiliary respiratory gas supply line; and aremote end of each of the auxiliary respiratory gas supply line isconnected with a respiratory gas source for supplying a respiratory gasto a patient; wherein each head is sized to be snugly received andretained within one of the nasal cavities of the patient while forming asufficient leakage passage, between a portion of inwardly facing nasalcavity skin of a patient and a portion of an exterior surface of thehead, to facilitate exhausting of any excess respiratory gas supplied tothe patient through the leakage passage.

The present invention relates to a method of treating a patient withsleep disorder with a respiratory gas, the method comprising the stepsof: inserting prongs of a nasal cannula within respective nostrils ofthe patient; supplying a respiratory gas to the nasal cannula at aconstant flow rate sufficient to form a back pressure within thebreathing passageways of the patient, at least when the patient isexhaling; and allowing, at least during exhalation, a portion of thesupplied respiratory gas to leak from the nostril between the prongs ofthe nasal cannula and inwardly facing skin of the nostril.

The present invention relates to a diagnostic tool for measuring nasalcavity pressure of a patient, the diagnostic tool comprising a the nasalcannula comprising: a pair of supply lines which each have a head at oneend thereof with a discharge opening therein for discharging arespiratory gas, and the opposite end of each of the pair of supplylines being connectable to a respiratory gas source; each head beingsized to be snugly received and retained within one of the nasalcavities of the patient while forming a sufficient leakage passage,between a portion of inwardly facing nasal cavity skin of a patient anda portion of an exterior surface of the head, to facilitate exhaustingof any excess respiratory gas supplied to the patient through theleakage passage and sensing probe associated with each head; and each ofthe pressure sensing probe is coupled to supply a pressure reading to apressure sensing device.

The present invention relates to a method of using a diagnostic tool formeasuring nasal cavity pressure of a patient, the method comprising thesteps of: permitting a patient to sleep; monitoring the sleeping patientwith a diagnostic tool while a respiratory gas is supplied to a patientat a first flow rate; determining a pressure within the nasal cavity ofthe patient via a pressure sensing probe of the diagnostic tool; andadjusting the flow rate of the respiratory gas until an optimumrespiratory gas flow rate is achieved which generates a desired backpressure within the breathing passages of the patient so that thepatient uniformly breathes while sleeping.

As used in this patent application and in the appended claims, sleepapnea, obstructed sleep apnea, oxygen desaturation, and other relatedbreathing interruptions, etc., all herein after referred to as “sleepdisorder”.

As used in this patent application and in the appended claims, the term“constant flow rate” means that the supply of the respiratory gas to thepatient must be at a sufficient flow rate to be efficacious, e.g.,generate a desired back pressure within the breathing passageways of thepatient to facilitate breathing, not being excess so as to providediscomfort to the patient.

As used in this patent application and in the appended claims, the term“trough” means an opening, passageway, indentation or some otherexterior surface irregularity such as, for example, a channel, a groove,a slot, a flute, or the like which facilitates leakage, in either flowdirection, between the inwardly facing nasal cavity skin of a patientand the exterior surface of the head of the cannula.

As used in this patent application and in the appended claims, the term“supply line” means an arm, a conduit, a tube, a duct, a channel, orsome other confined flow path for supplying a respiratory gas from asource to a patient.

Other details, objects and advantages of the present invention willbecome apparent as the following description of the presently preferredembodiments and presently preferred methods of practicing the inventionproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the followingdescription of preferred embodiments thereof shown, by way of exampleonly, in the accompanying drawings where:

FIG. 1 is an enlarged elevational view of a portion of a cannulaassembly according to the present invention in operative position on apatient;

FIG. 2 is an elevational view of a complete cannula assembly accordingto the present invention in an operative position on a patient;

FIG. 3 is a rear elevational view of the cannula of the cannula assemblyaccording to the present invention;

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 of FIG.3 showing the relative position of the cannula of FIG. 3 when secured toa patient with its extensions inserted into the patent's nasal cavity;

FIG. 5 is a top plan view of the cannula of FIG. 3;

FIG. 6 is a block diagram of a respiratory therapy system including anasal cannula assembly according to the present invention;

FIG. 7 is a diagrammatic view of another embodiment of the respiratorytherapy system;

FIG. 8 is a block diagram of another embodiment of a respiratory therapysystem including a nasal cannula assembly according to the presentinvention;

FIG. 9 is a front elevational view of a variation of the nasal cannula;

FIG. 9A is a diagrammatic view of the nasal cannula of FIG. 9 in thedirection of section line 9A-9A of FIG. 9;

FIG. 9B is a diagrammatic front view showing the two heads of the nasalcannula received within the nostrils of a patient to define a pluralityof leakage passages therebetween;

FIG. 9C is a diagrammatic side view of FIG. 9B showing the one of thetwo heads of the nasal cannula received within the nostrils of apatient;

FIG. 10 is a front elevational view of another variation of the nasalcannula;

FIG. 10A is a diagrammatic view of the nasal cannula of FIG. 10 in thedirection of section line 10A-10A of FIG. 10;

FIG. 10B is a diagrammatic view showing the two heads of the nasalcannula received within the nostrils of a patient to define a pluralityof leakage passages therebetween;

FIG. 11 is a diagrammatic cross sectional view of a swivel for use withthe respiratory gas supply lines of the respiratory therapy system;

FIG. 12 is a front elevational view of a diagnostic tool incorporatedinto the cannula of the present invention;

FIG. 12A is a diagrammatic view of the diagnostic tool of FIG. 12 in thedirection of section line 12A-12A of FIG. 12;

FIG. 12B is a front elevational view of the diagnostic tool of FIG. 12showing each of the pressure sensing probe coupled to a separatepressure sensing device;

FIG. 13 is a diagrammatic view of a housing incorporating the variousinternal heating, moisturizing and control components of the respiratorytherapy system;

FIG. 13A is a diagrammatic view depicting the internal heating,moisturizing and control components of the housing of FIG. 13;

FIG. 13B is a diagrammatic cross sectional view of the post heater ofFIG. 13;

FIG. 14 is a diagrammatic longitudinal cross sectional view of a sectionof a corrugated tube or some conventional insulating wrap or materialfor the respiratory gas supply line;

FIG. 14A is a diagrammatic cross section view along section line 14A-14Aof FIG. 14;

FIG. 15 is a diagrammatic cross sectional view of a slip loop to controltensioning of the pair of auxiliary respiratory gas supply lines;

FIG. 15A is a diagrammatic top plan view of the slip loop of FIG. 15;

FIG. 16A is an enlarged elevational view of a cannula assembly,according to the present invention, in operative position on a patient;

FIG. 16B is an elevational view of a complete cannula assembly,according to the present invention, in an operative position on apatient;

FIG. 17 is a front elevational view of a variation of the nasal cannulawith a flow passage in the connecting bridge;

FIG. 17A is a diagrammatic view of the nasal cannula along section line17A-17A of FIG. 17;

FIG. 17B is a diagrammatic front view showing the heads of the nasalcannula of FIG. 17 received within the nostrils of a patient to define aplurality of leakage passages therebetween;

FIG. 17C is a diagrammatic side elevational view of FIG. 17B showing theone of the two heads of the nasal cannula received within the nostrilsof a patient;

FIG. 18A is a diagrammatic front view showing a system for securing thecannula assembly, according to the present invention, to a patient in anoperative position;

FIG. 18B is a diagrammatic side perspective view of the system of FIG.18A shown secured to a patient in an operative position;

FIG. 18C is a diagrammatic side perspective view showing the system ofFIG. 18A for securing the cannula assembly to a patient in an operativeposition;

FIG. 18D is a diagrammatic transverse cross sectional view of a gassupply line having a spiral reinforcing member contained therein;

FIG. 18E is a partial diagrammatic cross sectional view of the gassupply line of FIG. 18D along section line 18E-18E of FIG. 18D;

FIG. 19A is a diagrammatic view of an improved gas flow sensor;

FIG. 19B is a diagrammatic view of the cannula assembly having a gasflow sensor in an operative position on a patient; and

FIG. 20 is a diagrammatic view of the cannula assembly having a flowregulating mechanism in an operative position on a patient.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein like or similar references indicatelike or similar elements throughout the several view, a nasal cannulaassembly, according to the present invention, generally designated byreference numeral 10, is shown in FIGS. 1 and 2 in an operative positionon a patient's face. The nasal cannula assembly 10 comprises a nasalcannula 12, a pair of auxiliary respiratory gas supply lines 14connected to supply lines or arms 26 of the cannula (described below infurther detail), a main respiratory gas supply line 16, a connector 18for coupling each of the auxiliary lines 14 to the main respiratory gassupply line 16, an optional slip loop or line tightening member 20disposed about auxiliary lines 14 for facilitating adjustment of theauxiliary lines about the patient's ears and head, and an end connector22 for facilitating connection of a second end of the main respiratorygas supply line 16 to a pressurized respiratory or respiratory gassource 23. As described in greater detail below with reference to FIG.6, the pressurized respiratory or respiratory gas source 23 comprises acompressor for delivering pressurized air (such as is commonly used inthe treatment of OSA). Depending on a patient's therapeutic needs, arespiratory therapy system including the pressurized respiratory orrespiratory gas source 23 may deliver heated and humidified respiratorygas to a patient.

Cannula 12 is generally a unitary member that may be fabricated by anysuitable molding process such as, for example, by a dip molding process.Examples of dip molding processes for cannula formation include thosedisclosed in U.S. patent application Ser. Nos. 09/754,471 and09/883,843, now U.S. Pat. Nos. 6,533,983 and 6,533,984, respectively,(both of which are entitled “Method to Produce Nasal and Oral CannulaBreathing Detection Devices”) and the disclosures thereof areincorporated herein by reference in their entireties. The composition ofcannula 12 is preferably a thermoplastic composition such as polyvinylchloride, polyvinyl acetate, polyethylene, soft latex or other materialsthat are highly pliable or flexible.

As most clearly illustrated in FIGS. 1, 3, and 5, cannula 12 comprises anarrow or short-length central bridge member 24 which spaces apart apair of substantially right angle flexible supply arms 26. The ridges ofthe supply arms 26 are integrally connected to the central bridge member24 along opposite side end edges 28 thereof (as shown in FIG. 3) and thesecond ends of the supply arms 26 are respectively connectable to one ofthe auxiliary respiratory gas supply lines 14 (as shown in FIGS. 1 and2). The connection between supply arms 26 of cannula 12 and auxiliaryrespiratory gas supply lines 14 may be effectuated by any suitablemethod or means and the connection may be either releasable orpermanent. For example, according to a presently preferred embodiment,the supply arms 26 are intimately received within the auxiliaryrespiratory gas supply lines 14 and their connections may be maintainedby friction fit, a solvent, adhesive bonding, ultrasonic welding, etc.

As shown in FIGS. 4 and 5, a nozzle or hollow tubular extension 30 isintegrally formed with and project upwardly from the ridge of each ofthe supply arms 26. Each tubular extension 30 preferably assumes aslightly curved configuration, corresponding substantially to that of ananterior region of a patient's nasal cavity, and terminates in arespiratory gas discharge outlet 32. For optimum patient comfort, eachtubular extension 30 preferably tapers upwardly from the top of thecentral bridge member 24 to the discharge outlets 32. In operation, eachtubular extension 30 is inserted into one of the nostrils of the patientso as to extend into the nasal cavity N. The curved configuration of thetubular extensions 30 permits a positive guiding of the respiratory gassupply along the natural contours of the nasal passages into the pharynxP rather than toward the upper reaches of the nasal cavity where therespiratory gas may cause pressure and potentially irritate the patient.In addition, there are no sharp edges along or at the tip of the tubularextensions 30 which could irritate the nasal passage due to themovements induced by patient breathing and the soft, flexible materialof the cannula permits the extensions to easily conform to the contoursof the nasal cavity N.

Unlike some conventional nasal cannulas that possess structure whichspans most, if not all of a patient's upper lip, the central bridgemember 24 of cannula 12 is quite narrow and has a relatively short axiallength. Indeed, it is configured to span substantially no more than thewidth of the patient's philtrum 34 (FIG. 1). As a result, a minimal areaof the front surface of the patient's upper lip is in continuous contactwith a rear surface of the central bridge member 24 and the cannula 12during use of the cannula. Additionally, as shown in FIG. 4, the uppersurface of central bridge member 24 is preferably rounded in order tominimize the area of contact on the lower, outer surface of the nasalseptum and to avoid any sharp or straight edges that may concentratepressure thereagainst. Thus, the combination of these features causesthe cannula 12 to lightly contact a small portion of the nasal-labial ofthe patient, thereby enhancing both the comfort to a patient who mustwear a nasal cannula 12 for prolonged periods of time and the patient'swillingness to comply with his/her CPAP therapy program.

FIGS. 1 and 2 illustrate the preferred manner in which the cannulaassembly 10 is to be worn by a patient. The cannula 12 generally restsacross the patient's nasal-labial area while the flexible auxiliaryrespiratory gas supply lines 14 initially extend across the patient'sface, over and behind the patient's ears, down the haw areas and arebrought together under the chin of the patient. The line tighteningmember 20, which is of sufficient size to encompass both of theauxiliary supply lines 14, may then be adjusted along the length of theauxiliary supply lines 14 so that the cannula 12 will remain firmly inplace without the auxiliary supply lines 14 being uncomfortably taut onthe patient.

As depicted in FIG. 5, the central bridge member 24 of cannula 12,according to one construction, defines a horizontal plane X. Each of thesupply arms 26 lie on one side of the horizontal plane X and lie in arespective horizontal plane X′ that forms an acute angle a relative tothe horizontal plane X of the central bridge member 24. Disposing thesupply arms 26 at an angle α, with respect to the horizontal plane X ofthe central bridge member 24, serves to minimize the amount of tensionand/or force that must be applied to the auxiliary respiratory gassupply lines 14 to maintain the cannula 12 in position against thepatient's nasal-labial.

Additionally, as shown in FIG. 3, the opposite end of each of the supplyarms 26 initially extends away from the ridge and the central bridgemember 24 and then bends and turns outwardly away from one another tothe second end in a gently curved configuration having a radius ofcurvature of about 0.4 inch to about 0.8 inch depending on the facialcharacteristics and head size of the patient that will use the device,e.g., child or adult. Although supply arms 26 are highly flexible andyieldable they nevertheless possess sufficient resilience or stiffnessto impart a desirable configuration to the auxiliary supply lines 14which further enhances the patient's comfort. That is, the curved supplyarms 26 function to urge the auxiliary respiratory gas supply lines 14to pass beneath and around, rather than across or over, the patient'scheekbone areas 36 (FIG. 1). This arrangement advantageously avoids thediscomfort that some patients experience when the nasal cannulaauxiliary respiratory gas supply lines contact their cheekbone areas 36.Thus, when the nasal cannula assembly 10 of the present invention issubjected to the pulling force of the auxiliary respiratory gas supplylines 14 when the assembly is worn by a patient (which pulling force isgreater for larger caliber and stiffer auxiliary respiratory gas supplylines that are designed to deliver high respiratory gas flows), itexerts minimal pressure against both the patient's nasal-labial 34 andcheekbone areas 36.

As mentioned above, the nasal cannula assembly 10 is beneficial whetherit is used to convey respiratory gases under low flow rates, such asmight be administered for oxygen assistance therapy, or high flow ratesof at least about 120 liters per minute, as might be required forpositive airway pressure administration for treatment of OSA. In anyevent, the dimensions of the main respiratory gas supply line 16, theauxiliary respiratory gas supply lines 14 and the cannula supply arms 26will be optimized to provide minimum bulk and weight, minimal pressuredrop, maximum flow and minimum turbulence and noise generation. Inaddition, it will be understood that the nasal cannula 12 may be moldedto any dimensions suitable to accommodate the particular physical facialcharacteristics and sizes of a patent ranging in size from very smallchildren or infants to very large adults. The result is a highlycomfortable assembly that can be worn by a patient for long periods oftime even under conditions of high gas flow rates whereby the patient ismore likely to comply with and obtain the optimum benefits of his or herrespiratory therapy regime.

FIG. 6 illustrates, in general, a respiratory therapy system 40including a pressurized respiratory or respiratory gas source 23 forsupplying the respiratory gas to the system 40 and the patient P, and anasal cannula assembly 10 according to the present invention. Therespiratory therapy system 40, described in further detail below, can begenerally defined as an open system providing a high flow of arespiratory gas to the patient P. An open system is generally open tothe effects of ambient air pressure. As is readily apparent to oneskilled in the art, this occurs adjacent the discharge opening 32 of thenasal cannula assembly 10 where the respiratory gas flow is introducedinto the nostrils of the patient's nose and a portion of the respiratorygas along with a portion of the exhaled gases of the patient, is allowedto leak out through the nostril/tubular extension interface.

In contrast to the open respiratory therapy system 40 of presentinvention, the previously known sleep apnea gas delivery systems are, ingeneral, closed systems which provide a respiratory gas at a specifiedhigher pressure relative to the ambient air pressure. In such closedsystems, a face mask is sealed over the mouth and/or nose of the patientP, thus creating the closed pressure system. A closed gas deliverysystem may generate pressures in the range of 4 to 20 cm H₂O in thepatient's respiratory passages to maintain open airways. The sealed maskis, of course, worn by the patient while he/she is sleeping. However,the sealed mask and the pressure developed thereby with the deliveredrespiratory gas are particularly uncomfortable to the patient and thetreatment is often prematurely abandoned by the patient after severalsessions due to a variety of reasons, e.g., discomfort of the mask, etc.

In many cases of sleep apnea, the burden and effect of such closedsystems is not necessary. The open respiratory therapy system 40 of thepresent invention overcomes the above noted drawbacks of known closedtherapy systems. The above described nasal cannula assembly 10 issubstantially more comfortable for the patient to wear then the masksused in known sleep apnea treating systems. Thus, the patient is lessapt to remove the mask and forego the therapy due to discomfort. Thedelivery of a high flow of respiratory gas to the patient's airwaysensures that there is an abundance of the respiratory gas available tothe patient which is delivered at 4 to 20 cm of H₂O pressure.

In general, as shown by the heavy black arrows of FIG. 6 as well as inFIG. 7, the respiratory therapy system 40 of the present inventionsupplies a respiratory gas from a source 23 to an initial gas flowdeveloping/measuring mechanism 44 for imparting a desired high flow rateof the respiratory gas through a remainder of the respiratory therapysystem 40 to the nasal cannula assembly 10 and into the patient's upperrespiratory system. The high flow rate permits the patient's lungs tofreely draw in the respiratory gas, and the high flow rate ofrespiratory gas provides a rich, abundant source of the respiratory gaswithout the need for developing a significant over pressure in thepatient's lungs by using a mask to cover the patient's mouth and nose.The flow developing/measuring mechanism 44, for developing the desiredrespiratory gas flow rate, can be, for example, a compressor, a fan, apump, a blower or some other conventional device which is well known inthe art. The flow developing/measuring mechanism 44 typically willsupply the respiratory gas at a rate of from about 20 to about 120liters per minute, preferably about 50 liters per minute, at a pressureof from between 4 and 20 cm of H₂O.

The respiratory gas generally is conditioned prior to delivery of thesame to the patient. Generally a humidifier 50 is provided forconditioning the respiratory gas prior to delivery to the patient. Therespiratory gas is typically warmed and humidified in order to minimizeand/or avoid patient discomfort and possibly harm to the internaltissues of the patient's nasal cavity. In particular, respiratory gassupplied at the above described flow rates should be maintained at arelative humidity of about 70 percent and 100 percent and morepreferably at a relative humidity of about 80 percent. Additionally, thetemperature of the supplied gas should be within the range of about 81°F. (27.2° C.) and about 90° F. (32.2° C.) and more preferably at atemperature of about 86° F. (30.0° C.).

High flow conditions may also tend to create noise and turbulence in theauxiliary gas supply lines 14 and/or the supply arms 26 which may causeannoyance and/or discomfort to the patient and may be detrimental to thepatient's long term use of the system. In order to minimize noise andturbulence, the components of the nasal cannula assembly 10, theauxiliary respiratory gas supply lines 14 and the main respiratory gassupply line 16 typically have an inner diameter of about 0.173 to 0.290inch (0.439 to 0.736 cm) and an outer diameter of about 0.350 inch(0.889 cm), although other sizes are also contemplated and would bereadily apparent to those skilled in the art. It is also possible toutilize ribbon supply conduit as long as the respiratory gas supplylines are sufficiently sized to satisfy the gas delivery conditions andprevent or minimize kinking thereof.

In the case of a specially prepared respiratory gas, a check valve orsome other suitable supply gas metering device 46 is preferablyprovided, as part of the respiratory gas source 42, to conserve use ofthe respiratory gas. The respiratory gas is thus supplied via themetering device 46 to the flow developing/measuring mechanism 44. Theflow developing/measuring mechanism 44 typically supplies therespiratory gas to the humidifier 50, for adequately humidifying therespiratory gas, and then to the heater 47, for adequately heating therespiratory gas, before finally supplying the same via the nasal cannulaassembly 10 to the patient P.

A controller 56 is used to control the flow parameters of therespiratory therapy system 40, e.g., monitor the desired flow, asselected by the user, or as required by the ramp or re-ramp functions.The controller 56 provides adjustment for varying the respiratory gasflow rate from about 20 to 120 liters per minute, preferably about 50liters per minute, over a period of from about 5 minutes to 30 minutes,to enable the patient to acclimate to the desired flow rate (rampfunction). This ramp function can be used for both initial cold startupsand hot interrupted sleep starts.

Additionally, the controller 56 continuously monitors the respiratorygas temperature and provides an input to the humidifier 50 and theheater 47 to control individually both the humidity and/or temperatureof the supplied respiratory gas. The controller 56 also monitors andprovides control of the temperature throughout the ramp functions so asto maximize patient comfort. The controller 56 is provided with controllogic circuits to monitor and control these various aspects of therespiratory therapy system 40 and as such control logic circuits areconventional and well known in the art, a further detail discussionconcerning the same is provided.

A number of other devices may also be provided to supply differentinputs to the controller 56. For example, an ambient temperature sensor66 may supply the ambient temperature to the controller 56 to optimizethe temperature of the respiratory gas relative to the patient's ambienttemperature surroundings. Also, the respiratory therapy system 40 mayinclude an ambient humidity sensor 67 for sensing the ambient humidityto assist with a more effective control of the humidity of therespiratory gas leaving the humidifier 50.

In a still further embodiment of the present invention, as shown in FIG.8, the respiratory therapy system 40 may provide the respiratory gas,either before or after passing through 120 liters per minute, preferablyabout 50 liters per minute, a flow developing/measuring mechanism 44,through a pass over humidifier 70, or some other type of humidifierknown in the art provided with variable heat control to more efficientlymanage humidification and increase water vapor in the respiratory gas.The humidified respiratory gas is then conveyed to a heater (e.g., apost heater) 48 and subsequently supplied to the nasal cannula assembly10 for delivery to the patient P. Again, as discussed above, thecontroller 56 is used to monitor and control the system components,namely, the flow developing/measuring mechanism 44, the humidifier 70and the heater (e.g., a post heater) 48 to adequately control thetemperature and humidity of the respiratory gas before delivery to thepatient. A temperature measurement sensor 58 may be provided in therespiratory therapy system 40, after the heater (e.g., a post heater)48, and the ambient room temperature sensor 66 and the ambient roomhumidity sensor 67 may provide the controller 56 with inputs to assistwith ensuring that the respiratory gas is controlled at a desiredtemperature and humidity level prior to delivery to the patient P.

Preferably the respiratory gas, once being sufficiently heated andhumidified by the respiratory therapy system 40 just prior to deliveryto the patient, typically is delivered at a relative humidity of between70 and 100 percent and more preferably a relative humidity of about 85percent.

With respect to heating of the respiratory gas, a post heatingarrangement is preferred as it heats up and cools down relativelyquickly thereby facilitating more accurate control of the temperature ofthe respiratory gas being supplied to the patient.

With reference to FIGS. 9-9C, a further variation of the invention willnow be described. As this embodiment is quite similar to the previousembodiment, only the differences between this embodiment and theprevious embodiment will be discussed in detail. According to theembodiment, the prong end of each supply arm 26 includes an enlargedhead 72 which contains the respiratory gas discharge outlet 32. The head72 preferably has an elliptical transverse cross sectional shape (seeFIGS. 10-10B) which facilitates both insertion and removal of the head72 as well as retention thereof within the nostril of the patient. Themaximum diameter of the elliptically shaped head may be slightlycompressed as the head 72 is received within in the respective nostriland such slight compression of the head 72 leads to improved retentionof the head 72 within the nostril without any perceived discomfort tothe patient. Alternatively, the diameter of the head 72 may besubstantially cylindrical in shape as is shown in FIGS. 7-9C. At leastone and preferably a plurality of equally spaced apart elongatechannels, grooves, slots, troughs or flutes 74 are formed in theexterior surface of the head 72. Each one of these elongate channels,grooves, slots, troughs or flutes 74 extends substantially parallel to,but is spaced from, a longitudinal axis A of the tubular extension 30 tofacilitate exhausting of any excess supplied respiratory gas from thenasal cavity as well as permitting inhalation by the patient of anyrequired additional air needed by a patient during inhalation. Eachelongate channel, groove, slot, trough or flute 74 generally is definedby a pair of adjacent side surfaces 75, diverging from a common elongatevalley 76, toward the pair of adjacent elongate ridges 78. In the firstversion of the head 72 (e.g., the larger model) shown in FIGS. 9-9B, thehead 72 has a maximum outer diameter of between about 0.50 of an inch(1.3 cm) and about 0.70 of an inch (1.8 cm), preferably about 0.60 of aninch (1.5 cm) and has an axial length of between about 0.5 of an inch(1.3 cm) and about 0.60 of an inch (1.5 cm), preferably about 0.55 of aninch (1.4 cm) so that the head 72 is readily received and retainedwithin a nostril 71 of a patient having a relatively large nostril (seeFIGS. 9B and 9C). According to this embodiment, the enlarged head 72 haseight elongate channels, grooves, slots, troughs or flutes 74 equallyspaced about the circumference of the head 72. Each valley 76 has adepth of between about 0.03 of an inch (0.08 cm) and about 0.06 of aninch (0.15 cm), preferably about 0.05 of an inch (0.13 cm).

According to a second version of shown in FIGS. 10-10B, e.g., a“smaller” version of the enlarged head 72, the head 72 has a maximumouter diameter of between about 0.345 of an inch (0.88 cm) and about0.375 of an inch (0.95 cm), preferably about 0.355 of an inch (0.90 cm)and has an axial length of between about 0.30 of an inch (0.76 cm) andabout 0.375 of an inch (0.95 cm), preferably about 0.35 of an inch (0.9cm) so that the head 72 is readily received within a nostril 71 of apatient having relatively a smaller sized nostril (see FIG. 10B).According to this embodiment, the enlarged head 72 has six elongatechannels, grooves, slots, troughs or flutes 74 equally spaced about thecircumference of the head 72. Each valley 76 has a depth of betweenabout 0.015 of an inch (0.04 cm) and about 0.035 of an inch (0.09 cm),preferably about 0.025 of an inch (0.06cm).

It is to be appreciate to those skilled in this art that numerousvariations concerning the number, the shape, the depth, the width, thesize, the cross sectional leakage area, etc., of the elongate channels,grooves, slots, troughs or flutes 74 and leakage passageways 81 would bereadily apparent to those skilled in the art depending upon theparticular application. In view of this, a further detail descriptionconcerning such variations and/or modifications of the enlarged head 72,the side surfaces 75, the valleys 76, the elongate ridges 78 and/or theleakage passageway 81 is not provided herein but such numerousvariations are considered to be within the spirit and scope of thepresent invention.

As the ridge of the nasal cannula 12 is received within the respectivenostrils 71 of a nose 73 of the patient (see FIGS. 9B, 9C and 10B), theelongate valleys 76 of the nasal cannula 12 have a diameter which aresized to be slightly smaller than the perimeter opening of the nostril71 of the patient so that a plurality of circumferentially spacedleakage passageways 81 are formed. Each one of the leakage passageways81 is formed and defined by the pair of adjacent side surfaces 75,diverging from a common elongate valley 76 toward the pair of adjacentelongate ridges 78, and the inwardly facing skin tissue 69 of thenostril 71. For the large head 72 (see FIGS. 9-9B), the adjacent sidesurfaces 75, diverging from a common elongate valley 76, and theinwardly facing skin tissue 69 of the nostril 71 together define a crosssectional open area or leakage passageway 81 of between about 0.0045square inches (0.029 cm²) and 0.0055 square inches (0.035 cm²), andpreferably define a cross sectional open area or leakage passageway 81of about 0.005 square inches (0.032 cm²). For the smaller head 72 (seeFIGS. 10-10B), the adjacent side surfaces 75, diverging from a commonelongate valley 76, and the inwardly facing skin tissue of the nostril71 together define a cross sectional open area or leakage passageway 81of between about 0.002 square inches (0.013 cm²) and 0.003 square inches(0.019 cm²), and preferably define a cross sectional open area orleakage passageway 81 of about 0.0025 square inches (0.016 cm²).

The head 72 is sized to facilitate retention of the nasal cannula 12within a nostril 71 of a patient while the leakage passageways 81prevent a fluid tight seal from being formed, between the exteriorsurface of the enlarged head 72 of the nasal cannula 12 and the inwardlyfacing skin tissue 69 of the patient's nostril 71, so as to continuouslyallow any excess respiratory gas supplied to the nasal cavity to beexhausted out therethrough. The leakage passageways 81 also continuouslyallow room air to flow inwardly therethrough in the event thatadditional air, for breathing by the patient in excess to the constantflow rate of the respiratory gas currently being supplied by therespiratory therapy system 40, is required during inhalation, e.g., at apeak negative pressure generated by the patient during inhalation. Bythis arrangement, the respiratory therapy system 40 is able to generatea sufficient resistance or back pressure within breathing passages ofthe patient, during exhalation, so that the breathing passages of thepatient remain adequately open and/or inflated without significantlyincreasing the work required by the patient during each inhalation andexhalation breath.

As is known in the art, a normal human being typically has a blood O₂concentration level of between 94% and 97%. One major respiratoryproblem plaguing numerous human beings worldwide is commonly known assleep apnea, e.g., a condition where the O₂ concentration level in thepatient's blood is about 88 percent or less.

The respiratory therapy system 40, according to the present invention,is readily able to treat both mild and moderate OSA and is alsosuccessful in treating severe OSA. During operation of the respiratorytherapy system 40, the gas supply flow rate remains constant during theentire treatment period. That is, the respiratory therapy system 40 doesnot vary the flow rate of the supplied respiratory gas due to anyvariation in the leakage of the system as typically occurs with theprior art devices and systems. Nevertheless, the supplied flow rate ofthe supplied respiratory gas is sufficient to dilute and/or diffuse theCO₂ which is in the process of being exhaled by the patient, during anexhalation breath, while still maintaining an adequate resistance orback pressure in the patient's breathing passages so that the bronchi,the trachea, the lungs, etc., all remain sufficiently inflated duringexhalation and upon commencement of a subsequent inhalation breath tothereby facilitate a more complete discharge or exhausting of theexhaust or byproduct gases, e.g., CO₂, from the patient while stillmaintaining a relatively low work of breathing for the patient duringinhalation.

The respiratory therapy system 40 typically delivers the respiratory gasat a flow rate of between about 20 and about 120 liters per minute,preferable about 50 liters per minute at a pressure of between about 4to 20 cm of water. Such flow conditions of the respiratory gas aregenerally adequate to create and maintain a sufficient back pressure inthe breathing passages of the patient so that the breathing passagesremain sufficiently open and do not collapse, during an exhalationbreath of a patient. It is to be appreciated that if the breathingpassages of the patient collapse, such collapse tends to preventcomplete exhalation of CO₂ and/or any other patient byproduct gases andthereby traps the same within the breathing passages of the patient.Since, according to the present invention, the breathing passages of thepatient are essentially prevented from collapsing and/or becomesufficiently obstructed, during the exhalation, the normal gas exhaustairway passages, from the alveoli to the nasal cavity of the patient,remain sufficiently open, unconstricted and/or unobstructed duringexhalation whereby any CO₂ and/or any other patient byproduct gasestransferred to alveoli, from the blood stream of the patient, is able toflow along this normal gas exhaust airway passages and be exhaled by thepatient during an exhalation breath.

Due to the higher delivery rates of the present invention, e.g., 20 to120 liters per minute, for example, the respiratory therapy system 40 isprone to generate noise as the respiratory gas is supplied along themain respiratory gas supply line 16, the auxiliary gas supply lines 14,the supply arms 26 and/or the heads 72 to the patient. It is desirableto design the respiratory therapy system 40 to minimize generation ofnoise, during operation of the respiratory therapy system 40, to a noiselevel of less than 50 decibels or so and more preferably to reduce thegeneration of noise, during operation of the system, to a noise levelapproaching about 46 decibels or so. In order to achieve such areduction in noise, it is important that the main respiratory gas supplyline 16, the auxiliary respiratory gas supply lines 14, the supply arms26 and the head 72 all have gradually bends, transitions, expansions andcontractions along the respiratory gas flow path. That is, all of therespiratory gas supply lines, conduits, tubes, duct, channels,components, etc., must avoid any sharp, acute or right angle bends,turns or curvatures and also avoid any rapid expansion and contractionof the gas supply lines, conduits, tubes, duct, channels, components,etc.

The reduction in noise is particularly important as the nasal cannula12, according to the present invention, is typically utilized at nightwhile the patient is sleeping. To further reduce the noise, thetransition from the supply arm 26 to the tubular extension 30 can have agradual increase in dimension so that there is more gradual expansion ofthe respiratory gas that enters into the tubular extension 30 and thiswill further assist with reducing the noise associated with therespiratory gas conveyed to the patient.

To further assist with providing comfort to a patient utilizing therespiratory therapy system 40, a 360 degree rotatable swivel 80 (seeFIG. 11) may be provided, along the main respiratory gas supply line 16,for example, to facilitate rotation of the nasal cannula assembly 10relative to a remainder of the respiratory therapy system 40. Apreferred location for the swivel 80 is at a location closely adjacentthe connection of the main respiratory gas supply line 16 with theconnector 18 which, in turn, is coupled to the pair of auxiliaryrespiratory gas supply lines 14. A first end portion 82 of a stationaryhousing 84 of the swivel 80 encases or is received within the opening inthe remote end of the main respiratory gas supply line 16. Preferably,the first end portion 82 of the stationary housing 84 is glued, welded,or otherwise fixedly secured or attached to the main respiratory gassupply line 16 to prevent inadvertent removal or disconnectiontherefrom.

The rotatable swivel 80 further includes a rotatable housing 90 which ishas a first end 85 which is received by and encases the second endportion 86 of the stationary housing 84. A second end portion 89 of therotatable housing 90 either encases or is directly received within anopening of the connector 18. Alternatively, a short supplemental sectionof the main respiratory gas supply line 16 (not shown) may interconnectthe swivel 80 with the connector 18. An intermediate region of therotatable housing 90, between the first and second end portions thereof,includes a small bend 88 of about 10 to about 45 degrees, preferablyabout 20 degrees or so.

The first end 85 of the rotatable housing 90 and the second end portion86 of the stationary housing 84 each have a cooperating or matingcomponents which retain the rotatable housing 90 in permanent engagementwith the second end portion 86, e.g., by mating bearing surfaces or someother conventional arrangement, while still allowing relative rotationbetween those two components. The first end 85 of the rotatable housing90 includes an integral shoulder 92 while the second end portion 86 ofthe stationary housing 84 includes an integral shroud 94 with acooperating shoulder 96. A fluid tight gasket or seal 98 is sandwichedbetween the two shoulders 92, 96 to provide a seal which prevents anytreating respiratory gas from leaking thereby. The shroud 94 enclosesthe gasket or seal 98 to minimize any damage thereto by the externalenvironment. A snap locking ring 99 has a protrusion which engages withan annular recess provided in the exterior surface of the shroud 94 tocaptively retain the rotatable housing 90 on the stationary housing 84while still allowing relative rotation between those two components.

The pair of auxiliary respiratory gas supply lines 14 are connected toan opposite end of the connector 18 and the swivel 80 permits rotationof the nasal cannula, the pair of auxiliary respiratory gas supply lines14, the connector 18 and the rotatable housing 90 relative to thestationary housing 84, the main respiratory gas supply line 16 and aremainder of the respiratory therapy system 40. It is to be appreciatedthat a variety of modifications and changes may be made to the swivel80, as would be readily apparent to those skilled in this art, withoutdeparting from the invention. Such modifications and changes areconsidered to be within the spirit and scope of the present invention.

With reference now to FIG. 12, a diagnostic tool 113 which is useful inmeasuring the nasal cavity pressure, during both patient inhalation andexhalation and is particularly suited for use in a sleep lab, will nowbe described. The diagnostic tool 113 generally comprises, for example,either a “large” or a “small” nasal cannula 12 discussed above withreference to FIGS. 9-10B but with a modification. The head 72 located atthe ridge of each one of the ridges of the supply arms 26 supports apressure sensing hollow tube or probe 114 which is either permanentlysecured thereto, e.g., glued or otherwise fastened thereto, oradjustably secured thereto in order to facilitate adjustment of theexposed length of the pressure sensing hollow tube or probe 114 relativeto the respiratory gas discharge outlet 32. The pressure sensing hollowtube or probe 114 preferably enters through a rear end wall of the head72 and passes within and through the interior space of the head 72 alongan undersurface of one of the ridges 78 and two adjacent side surfaces75 which converge at that ridge 78 (see FIG. 12A). The pressure sensinghollow tube or probe 114 preferably exits through a front end wall ofthe head 72 and extends parallel to the longitudinal axis of the ridgeof the supply arm 26 away from the respiratory gas discharge outlet 32deeper into the nasal cavity of the patient during use than a remainderof the nasal cannula. The exposed length of the pressure sensing hollowtube or probe 114, relative to the respiratory gas discharge outlet 32,typically ranges between 0.280 of an inch (0.71 cm) and 0.670 of an inch(1.70 cm), regardless of whether or not the pressure sensing hollow tubeor probe 114 is permanently fixed to or adjustable relative to the head72, and more preferably the exposed length of the pressure sensinghollow tube or probe 114, relative to the respiratory gas dischargeoutlet 32, is about 0.52 of an inch (1.32 cm). Due to such spacing orpositioning of the pressure sensing probe 114, each one of the pressuresensing probes 114 is suitably located at desired position within thenasal cavity to more reliably detect a nasal cavity pressure reading. Inthe event that the position of the pressure sensing probe 114 relativeto the respiratory gas discharge outlet 32 is adjustable, this tends tofurther facilitate more reliably detection of a pressure reading withinthe nasal cavity.

The opposite end of each one of the pressure sensing probe 114 are bothcoupled to supply a pressure reading to a single common pressure sensingdevice 115 (see FIG. 12), such as a transducer manufactured by KorrMedical Technologies, Inc. of Salt Lake City, Utah under the RSS 100trademark/trade name or a handheld transducer manufactured by of BraebonMedical Corporation of Ogdensburg, N.Y. Alternatively, the opposite endsof each one of the pressure sensing probe 114 may each be coupled to aseparate pressure sensing device 115 (see FIG. 12B) for measuring thepressure of each one of the nostril cavities of the patient. Preferably,the conduit or tubing, of the pressure sensing probe 114, has an outsidediameter of between 0.068 of an inch (0.173 cm) and 0.070 of an inch(0.178 cm) or so in order to minimize any disruption of the respiratorygas flow through the interior space located within the head 72 of thenasal cannula assembly 10. As the pressure sensing probes 114 passthrough the head 72, it generally does not disrupt or alter the normalachieved leakage interface between the exterior surface of the enlargedhead 72 and the inwardly facing skin tissue 69 of the patient's nostril71.

The diagnostic tool 113 is particularly adapted to be utilized totitrate and determine a desired back pressure within the breathingpassages of the patient so that the breathing passages remainsufficiently open during both inhalation and exhalation. It is to beappreciated that the leakage passages 81, formed by each pair ofadjacent side surfaces 75, diverging from a common elongate valley 76,and the inwardly facing skin tissue of the nostril 71, will typicallyvary from patient to patient, e.g., the leakage passages 81 for somepatients will be larger or smaller than the leakage passages 81 of otherpatients. Further the breathing passageways, the bronchi, the trachea,the lungs, the lung capacity, etc., for each patient also vary widely.

During titration of a patient, typically the patient is permitted tosleep and is monitored with the diagnostic tool 113 while a respiratorygas is supplied to a patient at a first flow rate. The pressure withinthe nasal cavity of the patient is then determined by the pressuresensing probe 114 at this first respiratory gas flow rate. Dependingupon the determined pressure and the detected breathing characteristicsof the patient, the technician will then adjust the flow rate from therespiratory gas source 23 to vary, e.g., either increase or decrease,the flow rate of the respiratory gas being supplied to the patient. Foreach stepped increase or decrease of the respiratory gas flow rate, thetechnician continues to monitor the pressure generated within the nasalcavities of the patient and the breathing characteristics of the patientuntil the technician determines an optimum respiratory gas flow ratethat achieves a desired back pressure within the breathing passages ofthe patient so that the patient breathes adequately, especially whilethe patient is sleeping.

Following the use of the diagnostic tool 113, the patient will then havea reasonably good indication of the pressure within the breathingpassages of the patient which is required in order for the patient tobreath adequately, e.g., treat sleep apnea. Once the patient isevaluated with the diagnostic tool 113, the patient can then be suppliedwith or obtain a supply of similarly sized cannulas for use by thepatient. The patient can then install one of these similarly sizedcannulas on his/her respiratory therapy system 40 and adjust therespiratory gas flow rate to this previously determined flow rate sothat the patient will generate or create, within his/her breathingpassageways and lungs, a sufficient back pressure and thereby facilitatea more complete exhalation or exhaustion of any CO₂ and/or any otherpatient byproduct gases which are contained in the lungs and removedfrom the blood stream. It is to be appreciated that the diagnostic tool113 is not limited solely to CPAP applications but may be utilized for awide variety of breathing and/or diagnostic applications.

If desired, the respiratory therapy system 40 may be equipped with aclock 100 (only diagrammatically shown in FIGS. 13 and 13A) to displaythe current time to a patient using the respiratory therapy system 40.If desired, the clock may be equipped with an alarm to wake the patientat a desired wake up time in order to terminate supply or treatment ofthe respiratory gas after a desired treatment period. In addition, awater holding tank or reservoir 102 of the respiratory therapy system40, for facilitate adding humidity to the respiratory gas prior todelivery of the same to the patient, may be equipped with a low watersensor 104 coupled to an indicator (not shown in the drawings) toprovide either an auditory and/or a visual indication to the patientthat the water level within the reservoir 102 is low and requiresreplenishment. The reservoir 102 may also be equipped with a high watersensor 108 coupled to an indicator (not shown in the drawings) toprovide either an auditory and/or a visual indication to the patientthat the water level in the reservoir is in excess of the amount ofwater required for efficient operation of the respiratory therapy system40 and the patient should remove some water for more efficient operationof the respiratory therapy system 40. Lastly, the reservoir 102 may beequipped with a conventional water heater (not shown) to facilitateheating of the water contained therein. However, one problem associatedwith heating the water in the reservoir 102 is the generation of calciumcarbonate which has a tendency to plate out on the inner surface of thereservoir 102. This may also lead to possible calcium carbonate platingof the water heater thereby requiring periodic servicing of the waterheater. As each of the above features are conventional and well known inthe art, a further detail description concerning the same is notprovided.

To further insulate the heated and humidified respiratory gas from theambient environment, the main respiratory gas supply line 16 and/or theauxiliary respiratory gas supply lines 14 may be covered by or encasedwithin a plastic or corrugated tube or some conventional insulating wrapor material 112, e.g., a 10 mm corrugated tube 112. FIGS. 14 and 14Adiagrammatically show the main respiratory gas supply line 16 surroundedby or encased within the insulating wrap or material 112 or may possiblyhave a reinforcing member secured to or embedded within the mainrespiratory gas supply line 16 and/or the auxiliary respiratory gassupply lines 14. An insulating air pocket 111 is formed between theexterior surface of the main respiratory gas supply line 16 and theinwardly facing surface of the insulating wrap or material 112. Theinsulating wrap or material 112 helps to insulate the respiratory gasfrom the external environment of the respiratory therapy system 40 andhelp maintains the temperature of the respiratory gas substantially atthe initially heated and supplied temperature and also minimizes thepossibility of any humidity, added to the respiratory gas, condensingalong the inner surface of either the main respiratory gas supply line16, the connector 18, the swivel 80, the pair of auxiliary respiratorygas supply lines 14 and/or the nasal cannula.

As seen in FIG. 15, a slip loop or line tightening member 20 encasesboth of the auxiliary respiratory gas supply lines 14 to assist withapplying sufficient tension to the auxiliary respiratory gas supplylines 14 to maintain the heads 72 of the supply arms 26 adequatelypositioned within the nostrils 71 of the patient. Preferably the linetightening member 20 will have flared or enlarged mouth 120 and 122, atboth opposed ends thereof, but will have a smaller dimensionedintermediate section 124 for frictionally engaging with the exteriorsurface of both of the auxiliary respiratory gas supply lines 14. Theintermediate section 124 is sized to have a sufficient interference fitwith the exterior surface of the auxiliary respiratory gas supply lines14 so as to be retained along the auxiliary respiratory gas supply lines14 in any adjusted position. The frictional interference connection,between the intermediate section 124 of the line tightening member 20and the exterior surface of the auxiliary respiratory gas supply lines14, will maintain the line tightening member 20 at its adjusted positionwhile the flared mouths 120, 122 allow the auxiliary respiratory gassupply lines 14 to extend away from the line tightening member 20 andmove freely relative thereto without causing any sharp bend, kink orsome other obstruction or constriction in either of the auxiliaryrespiratory gas supply lines 14.

An important aspect of the present invention relates to providing avariable flow of a respiratory gas to a patient while also controllingthe amount of leakage escaping between the inwardly facing skin 69 ofthe nostril 71 of the patient and the exterior surface of the head 72 ofeach of the supply arms. This arrangement results in the breathingpassageways of the patient being sufficiently inflated during the entirebreathing process so that the passageways do not tend to constrict,collapse or otherwise obstruct relatively free breathing inhalation orexhalation of the patient.

Typically, the total combined length of the auxiliary supplied lines 14and the main respiratory gas supply line 16, once connected with oneanother, extends for a combined length of between 3 feet and 50 feet orso, and more preferably have a total combined length of about 7 feet.

The supplied respiratory gas provides the necessary resistance to thepatient, upon attempting an exhalation breath so that the breathingpassageway and lungs remain sufficiently inflated and thus do not have atendency to collapse, constrict or otherwise close or inhibit relativelyfree breathing during exhalation of the patient.

Due to the relatively high flow of the respiratory gas, the respiratorygas tends to dry out the nasal cavities and breathing passages of thepatient. As noted above, in order to combat this, the respiratory gas issufficiently humidified to a level approaching saturation while stillavoiding condensation of the added moisture along the main respiratorygas line 16, the auxiliary respiratory gas supply lines 14, the swivel80 and/or the connector 18.

In a preferred form of the invention, a temperature thermistor (notshown) may be located adjacent the connection of the main respiratorygas supply line 16 to the pair auxiliary respiratory gas supply lines14, at or adjacent the connector 18, to determine the temperature of therespiratory gas just prior to the respiratory gas being split into twoflow paths and conveyed to the nasal cannula assembly 10. Thisfacilitates more accurate control of the temperature of the respiratorygas being delivered to the patient.

To further assist with controlling the temperature and/or humidity ofthe respiratory gas being delivered to the patient, the system 40 may beequipped with a conventional look-up table which has the relativehumidities for different temperatures stored therein, i.e., it will beappreciated that the respiratory gas, depending upon its temperature,will have different relative humidities. The respiratory therapy system40 can then utilize this stored temperature and/or humidity informationto further optimize control of the humidity and temperature of thesupplied respiratory gas during operation of the system. As such look-uptables and utilization thereof are conventional and well known in theart, a further detailed description concerning the same is not provided.

To facilitate adding moisture to the respiratory gas, the respiratorygas is passed through a passover humidifier 116 (see FIG. 13B) where therespiratory gas passes around a serpentine or maze-like flow path 117from an inlet 118 to an outlet 119 thereof around a plurality of thebaffles 121 and an inwardly facing surface of an outer wall enclosingthe passover humidifier 116. The respiratory gas, as it passes by, overand/or through the passover humidifier 116, is sufficiently humidifiedto a desired humidity. However, one problem associated with using tapwater is the generation of calcium carbonate and/or other compoundswhich tend to plate out on and along the surface of the baffles 121and/or the inner surface of the reservoir and could also lead topossible plating of calcium carbonate and/or other compounds thereon. Ifdesired, as discussed above, the reservoir can be equipped with bothhigh and low water level alarms to notify the patient when service inthe reservoir is required.

The compressor supplies the respiratory gas to the reservoir where therespiratory gas will receive a sufficient quantity of moisture and isthen passed to along a respiratory supply line containing a heated wire.The heated wire extends along the length of the supply line and isheated to a desired temperature, e.g., between 27° C. and 32° C., toreduce condensation of the moisturized respiratory gas before themoisturized respiratory gas is conveyed to and inhaled by the patient.The temperature of the heated wire is controlled by a controller 56which controls the temperature thereof so that the respiratory gas isheated to a desired temperature. If necessary, the controller can turnoff the power to the heated wire entirely or shut the power off if itbecomes too hot due to the generation of excessive heat and then soundan alarm to notify the patient or other personnel that servicing of theheated wire is required. The respiratory gas, after passing through theheated wire, typically will have a relative humidity of between 70 and95 percent while it is preferable for the respiratory gas to have arelative humidity of up to 85 percent.

With respect to heating of the respiratory gas, a heated wirearrangement is preferred as it heats up and cools down relativelyquickly thereby facilitating more accurate control of the temperature ofthe respiratory gas being supplied to the patient.

If desired, the respiratory therapy system may also include arespiratory gas metering device (not shown) which facilitatesconservation of use of the respiratory gas during operation of therespiratory gas system. That is, the respiratory gas metering devicewill interrupt the constant flow of the respiratory gas to the patientfor a brief period of time, e.g., between breath when the patient isneither inhaling or exhaling, in order to conserve use of therespiratory gas. As such respiratory gas metering device, forinterrupting a constant flow of the respiratory gas to the patient for abrief period of time, is conventional and well known in the art, afurther detail discussion concerning the same is not provided.

Next considering still further alternate embodiments and implementationsof a respiratory therapy system 40 and nasal cannula assembly 10 of thepresent invention, FIGS. 16A and 16B is a diagrammatic representation ofan embodiment of a cannula assembly 126 providing an improved fit to thepatient's facial contours and an improved mechanism for supporting thecannula assembly 126 in the desired position with respect to thepatient's head, face and nasal passages.

As indicated in FIGS. 16A and 16B, the cannula assembly 126 is generallysimilar to the cannula assembly 10 previously described above withrespect to FIGS. 1, 2, 9, 9A, 9B, 9C10, 10A and 10B. As shown, the nasalcannula assembly 126 includes a nasal cannula 128, a pair of respiratorygas supply lines 130 connected to nasal cannula arms 132 of the cannula128, a main respiratory gas supply line 134, a connector 136 forcoupling each of the respiratory gas supply lines 130 to the mainrespiratory gas supply line 134, and an end connector 138 forfacilitating connection of a second end of the main respiratory gassupply line 134 to a pressurized respiratory or respiratory gas source140. The connection between the nasal cannula arms 132 and the auxiliaryrespiratory gas supply line source 140 may be effectuated by anysuitable method or means and the connection may be either releasable orpermanent. For example, according to an embodiment, the nasal cannulaarms 132 are intimately received and mate within ends of the respiratorygas supply lines 130 and their connections may be maintained by frictionfit, a solvent bonding, adhesive bonding, ultrasonic welding, etc.

As previously described and as will be discussed further below, thenasal cannula 128 is generally a unitary member that may be fabricatedby any suitable molding process such as, for example, by a dip moldingprocess. Examples of dip molding processes for cannula formation includethose disclosed in U.S. patent application Ser. Nos. 09/754,471 and09/883,843 (both of which are entitled “Method to Produce Nasal and OralCannula Breathing Detection Devices”) and the disclosures thereof areincorporated herein by reference in their entireties. The composition ofnasal cannula 128 is preferably a thermoplastic composition, such aspolyvinyl chloride, polyvinyl acetate, polyethylene, soft latex or othermaterials that are highly pliable or flexible.

As illustrated in FIGS. 16A and 17, for example, the nasal cannula 128includes a narrow or short-length central bridge member 142 which spacesapart the nasal cannula arms 132 from one another, with opposingparallel sides of. bridge member 142 being integrally connected to orformed as an integral part of nasal cannula arms 132. The bridge member142 defines an internal bridge flow passage 144 which provides aninterconnecting gas flow path between the spaced apart nasal cannulaarms 132 so that the bridge flow passage 144 generally operates toequalize the flow of gas from nasal cannula arms 132 to the two nasalpassages 146 and provides alternate flow paths from nasal cannula arms132 to the patient's nasal passages in the event that one or the otherof nasal passages 146 becomes partially or completely obstructed orrestricted for some reason.

Further considering the shape and configuration of nasal cannula arms132, as illustrated in FIG. 17 and as previously illustrated in FIGS. 9,9A, 9B and 9C, the prong end of each tubular extension 30 of each nasalcannula arm 132 includes an enlarged head 72 which contains therespiratory gas discharge outlet 32 in an end surface thereof. The head72 preferably has a somewhat elliptical transverse cross sectional shape(see FIGS. 10-10B) which facilitates both insertion and removal of thehead 72 as well as retention of the heads 72 within the respectivenostrils of the patient. The maximum diameter of the elliptically shapedhead may be slightly compressed as the head 72 is received within in therespective nostril and such slight compression of the head 72 leads toimproved retention of the head 72 within the nostril of the patientwithout any perceived discomfort to the patient. Alternatively, thediameter of the head 72 may be substantially cylindrical in shape.

As previously described, at least one and preferably a plurality ofequally spaced apart elongate channels, grooves, slots, troughs orflutes 74 are formed in and extend along the exterior surface of thehead 72. Each one of these elongate channels, grooves, slots, troughs orflutes 74 extends substantially parallel to, but is spaced from, alongitudinal axis of the tubular extension 30 to facilitate exhaustingexcess supplied respiratory gas from the nasal cavity. Again, eachelongate channel, groove, slot, trough or flute 74 is generally definedby a pair of adjacent side surfaces 75, diverging from a common elongatevalley 76, toward the pair of adjacent elongate ridges 78. As describedpreviously with reference to FIGS. 9, 9A, 9B and 9C and FIGS. 10, 10Aand 10B and described with regard to the larger and smaller exemplaryembodiments of the present invention, the dimensions of head 72 may varydepending upon the requirements of any specific use and/or patient. Itwill also be appreciated by those skilled in this art that numerousvariations concerning the number, the shape, the depth, the width, thesize, the overall shape and configuration, the cross sectional leakagearea, etc., of the elongate channels, grooves, slots, troughs or flutes74 and leakage passageways 81 would be readily apparent to those skilledin the art depending upon the particular application. In view of this, afurther detail description concerning such variations and/ormodifications of the enlarged head 72, the side surfaces 75, the valleys76, the elongate ridges 78 and/or the leakage passageway 81 is notprovided herein but such numerous variations are all considered to bewithin the spirit and scope of the present invention.

As discussed previously herein, the head 72 is sized to facilitatesecure retention of the nasal cannula 128 within a nostril 71 of apatient while the leakage passageways 81 prevent a fluid tight seal frombeing formed, between the exterior surface of the enlarged head 72 ofthe nasal cannula 128 and the inwardly facing skin tissue 69 of thepatient's nostril 71. For this reason, and in general according to thepresent invention, when the ridge of the nasal cannula 128 is receivedwithin the respective nostrils 71 of a nose 73 of the patient, theelongate valleys 76 of the nasal cannula 128 have diameters which aresized to be slightly smaller than the perimeter opening of the nostril71 of the patient so that a plurality of circumferentially spacedleakage passageways 81 are formed. This functional structure therebycontinuously allows excess respiratory gas supplied to the nasal cavityto be exhausted therethrough and out the nostril 71 of the patient. Dueto this arrangement, the respiratory therapy system 40 is able togenerate a sufficient resistance or back pressure within breathingpassages of the patient, during both inhalation and exhalation, so thatthe breathing passages of the patient remain sufficiently open and/orinflated without significantly increasing the work required by thepatient during each inhalation and exhalation breath.

Next considering the structure and configuration of respiratory gassupply lines 130 of this embodiment, as described above the nasalcannula arms 132 are connected to a respiratory gas source 140 via therespiratory gas supply lines 130. In the previously describedembodiments, a respiratory gas supply line 130 passed from each nasalcannula arm 32 and upwards and outwards across the corresponding cheek,over and around the patient's ear and back to a point under thepatient's chin, wherein the respiratory gas supply lines 130 areconnected to a common supply line 134 which is coupled to therespiratory gas source 140. This arrangement, however, can sometimescause some discomfort or irritation for the patient due to the weightand relative stiffness of gas supply lines 130 and the pressures on theears resulting from the support of cannula assembly 126 and the gassupply lines 130. In addition, the method of securing of gas supplylines 130, the connector 136 and the cannula assembly 126 in place bylooping the gas supply lines 130 over and around the ears sometimes doesnot provide the necessary security, particularly when the patient moveshis/her head or body or when the patient's head or body is moved bymedical personnel.

The embodiment of the invention illustrated in FIGS. 18A-18E, however,substantially alleviates or eliminates these problems by providing alighter, more flexible and more secure positioning of the cannulaassembly 126 and the gas supply lines 130. In this embodiment, asillustrated in FIGS. 18A-18E, the generally horizontal portion of theeach nasal cannula arm 132 is preferably somewhat shorter than in thepreviously illustrated embodiments, so that the connection interface148, between gas supply lines 130 and the corresponding nasal cannulaarms 132, are located relatively closer to the mid-line of the patient'sface and nose than with the previously illustrated embodiments of anasal cannula assembly 126. In the illustrated example, each connectioninterface 148 is located, in general, between the corresponding nose andmouth and in the region at or just outside an outer edge of the mouth.Such shortening of the nasal cannula arms 132, which are typicallymechanically more rigid than gas supply lines 130, allows the gas supplylines 130 have a curvature which begins closer to the mid-line of thepatient's nose, thereby allowing increased flexibility in routing thegas supply lines 130.

As illustrated in FIG. 18B, and referring for example to FIGS. 1 and 2for comparison, each gas supply line 130 has a first portion 130Acurving outwards and upwards from the connection interface 148 and so asto follow the surface of the cheek along a path below the cheekbone to afirst point 130B in a region generally below the outer corner of theeye. From the first point, each gas supply line 130 has a second portion130C that curves downwards and inwards along the surface of the cheekalong the jawline to a second point 130D between the outer corner of theeye and the ear. From the second point 130D, the gas supply line 130 hasa third portion 130E that curves inward below the jawline and forwardalong the side of the throat to a third point 130F below the chin andnear the mid-line of the face. The opposite gas supply line 130 is amirror image thereof and its third point 130F is also below the chin andnear the mid-line of the face. The two gas supply lines 130 then eachhave a fourth portion 130G that curve together toward one another anddownwards to connector 136 which connects the two gas supply lines 130to common gas supply line 134.

It can therefore be seen that according to this embodiment, the gassupply lines 130 define the contours of the edges of two planes, one foreach side of the patient's face and are joined between the nasal cannulaarms 132, wherein the contour lines defining the edges of the planesmore closely follow and conform to the contours of the patient's face.The structure defined by gas supply lines thereby conform to thepatient's facial contours somewhat like the outer edge of a form fittingmask, thereby more effectively supporting itself on the patient's faceand distributing a portion of the weight of the cannula assembly 126across the contours of the patient's face more evenly. The arrangementis thereby both more secure support by and secured to the face of apatient and is also more comfortable for the patient to wear.

In this regard, it must be further noted that the thickness of the wallsof bridge member 142 is similarly reduced to further reduce the weightof the cannula assembly 126 and provides greater flexibility in thejoint region between the two planes defined by gas supply lines 130,thereby allowing a closer, more comfortable and supportive and moresecure fit of the cannula assembly to the contours of the patient'sface.

As shown in FIGS. 18A and 18B, the gas supply lines 130 do not loop overand around the patient's ears to form loops holding the gas supply lines130 and the cannula assembly 126 to the patient's face. Instead, thepresent embodiment of the cannula assembly 126 includes both right andleft attachment straps or loops 150 in which each attachment strap orloop 150 includes an attachment strap or loop 150A, a fixed end fastener150B and an adjustable fastener 150C. At shown, one end of eachattachment strap or loop 150A is attached to a corresponding gas supplyline 130 by a fixed end fastener 150B that, in the exemplaryimplementation, is mounted onto the end of the gas supply line 130adjacent to the connection interface 148 of that gas supply line 130.The opposing end of each adjustable loop 150A adjustably engages with acorresponding adjustable fastener 150C that allows the length of theattachment strap or loop 150A, between the fixed end fastener 150B andthe adjustable fastener 150C, to be adjusted. As shown, the adjustablefastener 150C of each adjustable loop 150A is secured to the other gassupply line 130 at a point along the third portion 130E of that othergas supply line 130, that is, along that portion of the gas supply line130 that curves inward below the jawline and forward along the side ofthe throat to the point below the chin.

It will therefore be seen that the right and left attachment straps orloops 150, of the present embodiment, are arranged to cross over theback of the patient's head and in an X-configuration whereby eachattachment strap or loop 150 is anchored to opposite sides of thecannula assembly 126. As a result, the attachment between the cannulaassembly 126, the gas supply lines 130 and the other elements of thesystem are secure better than can be achieved by simple looping the gassupply lines 130 over and around the patient's ears. It will also benoted that this securing arrangement generally does not tug or pull onthe patient's ears, and more evenly distributes the pressures of holdingthe cannula assembly 126 and the gas supply lines 130 to the head of thepatient and thereby provides greater comfort for the patient. It shouldalso be noted that the crossing of the attachment straps or loops 150and the fact that the length of each attachment strap or loop 150 isseparately adjustable allows the attachment straps or loops 150 to be ofnon-symmetric lengths, such as may be required to accommodate otherequipment or, for example, dressings.

According to one embodiment of the attachment straps or loops 150, theadjustable loops 150A are of a generally circular or elliptical crosssection and may be either hollow or solid and either elastic ornon-elastic. The fixed end fasteners 150B are of the generally hollow,cylindrical or elliptical cross section and may be attached to gassupply lines 130 or, for example, to connection interfaces 148, or maybe formed or molded as integral parts of these elements. The adjustablefasteners 150C are likewise have a generally circular or ellipticaltransverse cross section and are hollow through their entire lengths sothat adjustable loops 150A can be inserted and pass through adjustablefasteners 150C to a desired adjustable length, with the inner diameterof the openings through adjustable fasteners 150C and the outerdiameters of the adjustable loops 150A being chosen to provide afriction fit that will securely hold adjustable straps or loops 150Awhile still allowing the length of the adjustable straps or loops 150Ato be readily adjusted. Again, the adjustable fasteners 150C may beattached to gas supply lines 130 or formed or molded as integral partsof gas supply lines 130, and the locations of fixed end fasteners 150Band adjustable fasteners 150C along gas supply lines 130 may be reversedfrom the illustrated positions.

Lastly, the adjustable straps or loops 150A, fixed end fasteners 150Band adjustable fasteners 150C may comprise, for example, a thermoplasticcomposition such as polyvinyl chloride, polyvinyl acetate, polyethylene,soft latex or other materials that are highly pliable or flexible. Inaddition, the attachment strap or loop 150 assembly may further includea generally X-shaped crossing connector 150D which may comprise, forexample, two hollow tubes attached to one another at a crossing midpointso that the two adjustable loops 150A can pass through the crossingconnector 150D and be separately adjusted without any interference fromone another. As indicated generally, the crossing connector 150D wouldbe positioned in the region where the two adjustable straps or loops150A cross over the back of the patient's head and functions to hold thetwo adjustable loops 150A in a fixed geometry with respect to oneanother, thereby further improving the comfort and security achieved bythis arrangement.

Next considering the detailed construction of gas supply lines 130, itis apparent from the above descriptions that the structural and thefunctional characteristics of the supply lines 130 are significantfactors in providing the benefits of the present invention. Asdiscussed, these benefits include, for example, increased security inmounting the nasal cannula 128 and associated supply lines to a patient,greater comfort for the patient, increased, easier gas flow to thepatient, and greater adaptability to a wider range of patient facialsizes and configurations, e.g., the cannula assembly 126 is readily ableto accommodate both child and adult patients as well as young adults,patients with round faces, patient with slim faces, patients with facesanywhere in between, etc.

An embodiment of an improved gas supply line 130, according to thepresent invention, is illustrated in FIGS. 18A-18E. As shown in FIGS.18C, 18D and 18E in particular, the supply line 130 comprises a tubinghaving an outside diameter generally similar to that used inconventional gas supply lines, but the diameter of the inside flowpassage is generally increased, over prior art designs, to provide agreater flow of respiratory gas therethrough with less flow resistancefrom the gas supply line 130. The gas supply line 130, according to thepresent invention, has an outside diameter of between about 0.65 inchesand 0.20 inches and an inside diameter of between 0.15 inches and 0.050inches. The gas supply line 130 is typically manufactured from, forexample, polyvinyl chloride, polyvinyl acetate, polyethylene, soft latexor some other material that is sufficiently pliable and flexible and hasa suitable chemical composition for the intended purposes.

In addition to increasing the internal gas flow capacity of gas supplylines 130 and being lighter than conventional gas supply lines, thedecreased wall thickness of gas supply lines 130 allows the gas supplylines 130 to be more flexible and mallable, thereby allowing gas supplylines 130 to more easily and closely follow and conform to the contoursof the patient's face and thereby result in a better, more secure andmore comfortable fit of the cannula assembly 126 for the patient. It isrecognized, however, that the decreased wall thickness of gas supplylines 130 may, in itself, result in a greater tendency for gas supplylines 130 to become more easily kinked, flattened, compressed orotherwise distorted when the line is manipulated or bent to followclosely the contours of the patient's face or when external force orpressure is applied to the lines such as, for example, when a patientturns his/her head so that one cheek sandwiches or compresses the gassupply line 130 against a pillow or mattress, for example.

To reduce or minimize this from occurring, the gas supply lines 130, asmore clearly illustrated in FIGS. 18D and 18E, includes a continuouselongate continuous spring-like spiral reinforcing member or spring 130Rwhich spirals within the side wall of the supply line 130 substantiallyalong the entire length of the supply line. The spiral reinforcingmember or spring 130R may be manufactured from a variety of differentmaterials such as steel, copper, brass, stainless steel, iron, forexample. As will be understood by those of skill in the relevant arts,the configuration of the spiral reinforcing member or spring 130R willprovide increased resistance and support against lateral or crosssectional distortion of the gas supply line 130, such as kinking at bendlocations along the gas supply line 130. At the same time, spiralreinforcing member 130R will not interfering with the longitudinalflexibility of the gas supply line 130, thereby allowing the gas supplyline 130 to freely conform and follow relatively tight bends and curves.In this regard, it is also preferable that the material of spiralreinforcing member 130R be sufficiently mallable such that the gassupply line 130 will remain in whatever shape or configuration that theline is bent or shaped into so that the gas supply line 130 can closelyfollow the desired contours of the patient's face and jawline.

It will therefore be recognized that the combination of mallable spiralreinforcing member 130R and the flexible tubing forming the wall of thegas supply line 130 are mutually supporting for the above discussedpurposes. That is, and as illustrated in FIGS. 18D and 18E, spiralreinforcing member 130R is essentially embedded into the wall of the gassupply line 130 or possibly recessed within or into a spiral grooveformed in the inner surface of the gas supply line 130. Such spiralgroove would assist with preventing the spiral reinforcing member 130Rfrom moving, slipping or distorting along the longitudinal axis of thegas supply line 130 during use. At the same time, the spiral reinforcingmember 130R, either embedded within or recess in a spiral groove alongthe inner surface of the gas supply line 130, reinforces the side wallof gas supply line 130 against lateral or cross sectional distortion. Itis to be appreciated that the cross section internal flow area of thegas supply line may be non circular (see FIG. 18D).

Preferably each section of the gas supply line either has an internalheating element or wire, extending along the length of the gas supplyline, or is suitably insulated to maintain the temperature of the heatedand moisturize gas, as it flows along the gas supply line, and minimizeany condensation of the moisture contained within the heated gas.

Lastly, as illustrated in FIGS. 19A and 19B, the invention furtherincludes an improved gas flow sensor 152 comprising a sensor element152S and a sensor controller 152C. The sensor element 152S comprises asingle thermistor located within a gas flow path along the gas supplyline 130. The sensor controller 152C, in turn, comprises a drive circuit152D for providing a controllable flow of current through the thermistorcomprising sensor element 152S, a measuring circuit 152M for measuringthe resistance of the sensor element 152S and thus the temperature ofthe thermistor, and a switching circuit 152X for alternately connectingthe drive circuit 152D and the measuring circuit 152M to the sensorelement 152S in a controllable duty cycle.

The basic mode of operation of gas flow sensor 152 is that the switchingcircuit 152X will alternately connect the drive circuit 152D and themeasuring circuit 152M to the sensor element 152S, according to a dutycycle whose duty cycle rate and duty cycle phase or pulse widths aredetermined by the switching circuit 152X. When the drive circuit 152D isconnected to the sensor circuit 152S, during the corresponding phase orpulse width of the switching circuit 152X duty cycle, the drive circuit152D drives pulses, of current at a known level and for a knownduration, through the thermistor forming sensor element 152S, therebyheating the thermistor to a known temperature so that the thermistorwill have a corresponding known resistance. The flow of gas over andpast the thermistor of the sensor element 152S will, however, removeheat from the thermistor at a rate determined by the flow of gas, thusproportionally lowering the temperature and the resistance of thethermistor by an amount proportional to the flow of gas. When themeasuring circuit 152M is connected to the sensor circuit 162S duringthe corresponding phase or the pulse width of the switching circuit 152Xduty cycle, the measuring circuit 152M will determine the volume of thegas flow by measuring the resistance of the thermistor forming thesensor element 152S.

In one implementation of the gas flow sensor 152, the duty cycle rateand the duty cycle phase or the pulse widths of switching circuit 152X,and the current supplied by the drive circuit 152D, are controlled by afeedback mechanism. In this implementation, the electrical energy andthus the heat driven into the thermistor, during the drive circuit 152Dpulse period of the switching circuit 152X, is controlled to be inbalance with the heat drained from the thermistor during the remainderof the duty cycle, which includes the measurement phase, so that thetemperature and thus the resistance of the thermistor remains constant.It has been shown empirically that when operated in this mode, the widthof the heating pulse phase of the switching circuit 152X duty cycle isnearly linearly proportional to the mass flow of the gas flowing pastthe thermistor of the sensor element 152S.

It will be recognized by those of skill in the relevant arts that thesensor element 152S need not be located directly physically adjacent thesensor controller, within reasonable limits that will be understood bythose skilled in the circuit design. It will also be understood that thethermistor forming the sensor element 152S can be relatively physicallysmall, so that the sensor element 152S can be located at any of a widerange of possible locations in a respiratory therapy system 40,depending upon where it is desired to measure a gas flow, and exemplarypossible locations are indicated in FIG. 19B.

Considering further embodiments and implementations of the presentinvention in further detail, it has been described herein that thepresent invention supplies a flow rate of respiratory gas to a patientthat is sufficient (a) to dilute and/or diffuse the CO₂ which is in theprocess of being exhaled by the patient during an exhalation breath and(b) to maintain a back pressure in the patient's breathing passages thatmaintains the breathing passages of the patient inflated. As described,the system and nasal cannula of the present invention therebyfacilitates a more complete discharge or exhausting of the exhaust orbyproduct gases from the patient while still maintaining a relativelylow work of breathing for the patient during inhalation and exhalation.According to the present invention, these objects are accomplished bythe creation of a sufficient back pressure, within the patient'sbreathing passages, which is caused by the flow of the respiratory gasthrough the flow resistance of the nasal cannula, particularly duringthe exhalation phase of the breathing cycle.

As described, the flow resistance through the nasal cannula isdetermined and controlled by the leakage passage(s) formed between theexterior surface of the heads of the nasal cannula and the matinginterior skin of the patient's nasal passage which allow the interiorbreathing passages of the patient to communicate with the exteriorenvironment of the patient. The back pressure is a direct function ofthe gas flow rate and the leakage passage flow resistance so that, for agiven leakage page flow resistance, the back pressure will be a directfunction of the gas flow rate and, for a given gas flow rate, the backpressure will be a direct function of the leakage path flow resistance.According to the present invention, therefore, the dimensions of theleakage passage and the gas flow rate are selected so as to maintain asufficient positive back pressure within the patient's breathingpassages so that the patient's breathing passages always remainadequately inflated during the entire breathing cycle and, inparticular, during exhalation.

As discussed herein above with regard to FIGS. 6, 7 and 20, therespiratory therapy system 40 of the present invention supplies arespiratory gas from a source 23 to a gas flow developing/measuringmechanism 44 that maintains a desired flow rate of the respiratory gasthrough the respiratory therapy system 40 to the nasal cannula assembly10 and into the patient's upper respiratory system. Again, and asdescribed, the flow rate is selected to permit the patient's lungs tofreely draw in the respiratory gas and to provide an adequate source ofthe respiratory gas to the patient without requiring the use of a maskto cover the patient's mouth and nose in order to provide the desiredover-pressure in the patient's lungs—the nasal cannula only communicateswith the patient's nasal passages.

The previously described flow developing/measuring mechanism 44 fordeveloping the desired respiratory gas flow rate can be, for example, acompressor, a fan, a pump, a blower or some other conventional devicewhich is well known in the art. The flow developing/measuring mechanism44 typically will supply the respiratory gas at a rate of from about 20to about 120 liters per minute, preferably about 50 liters per minute,at a pressure of from between 4 and 20 cm of H₂O. The gas flow rate iscontrolled by a controller 56 that controls the flow parameters of therespiratory therapy system 40, that is, monitors the desired gas flow asselected by the user or as required by the previously described ramp orre-ramp functions. In one implementation of the invention, thecontroller 56 provides adjustment for varying the respiratory gas flowrate from about 20 to 120 liters per minute, preferably about 50 litersper minute, over a period of from about 5 minutes to 30 minutes, toenable the patient to acclimate to the desired flow rate according tothe ramp function, which can be used for both initial “cold” startupsand as well as “hot” interrupted sleep starts.

In a first embodiment of the present invention as described hereinabove, the controller 56 maintains the gas supply flow rate at aconstant level through both the exhalation and the inhalation phases ofthe breathing cycle. In this first embodiment of the invention,therefore, and because the gas flow to the patient is constant, the gasflow rate out of the patient's respiratory passages and through theleakage passage will include a relatively constant average component,consisting of excess gas that is delivered to the patient but in excessof the patient's breathing requirements, and a variable componentresulting from the inhalation and the exhalation of the patient.

The variable component of gas flow outwards through the leakagepassage(s) will thereby increase during the exhalation phase and willdecrease, but remain slightly positive during the inhalation phase.Because it is desired that a positive back pressure exist in thepatient's respiratory passages at all times, it is therefore necessarythat there be a constant excess of gas supplied to the patient throughthe entire breathing cycle of the patient so that there always will be apositive flow or volume of excess gas escaping through the leakagepassage(s) at all times, thereby ensuring that there is a positive backpressure within the breathing passages of the patient at all times. Theconstant component of the gas flow rate to the patient must therefore beof a volume that exceeds the greatest negative excursion of the variablecomponent due to the patient's breathing so that there is always a netpositive volume of gas flow into the patient's respiratory system. Ifthis condition is met, there will be a positive outward gas flow of gasthrough the leakage path and a positive back pressure during all phasesof the breathing cycle, including both the exhalation and inhalationphases.

In an alternate embodiment, the gas flow rate to the patient is notconstant but is instead modulated generally in synchronization with thepatient's breathing cycle so as to maintain the back pressure at agenerally constant level, that is, so that the pressure in the patient'srespiratory passages is generally at a constant positive differentialrelative to the exterior room air pressure and does not varysignificantly with the patient's inhalation and the exhalation breathingcycle. It is preferable in the modulated gas flow embodiment, however,that the gas flow from source 140 to the supply line 134 be maintainedat a substantially constant flow volume due to technical and economicconsiderations in the design and the construction of gas flow source140. This embodiment of the present invention as shown in FIG. 20,therefore includes a flow regulating mechanism 154, in supply line 134or interposed between supply line 134 and nasal cannula assembly 126 orin nasal cannula assembly 128 itself, to modulate the gas flow to theheads 72 of nasal cannula 128, as necessary, to maintain a relativelyconstant pressure in the region of the discharge ends 30 of the heads 72of nasal cannula 128.

Before continuing with a detailed discussion of possible implementationsof a flow regulating mechanism 154, it must be noted that anyfluctuations in gas pressure, due to the varying resistance of thepatient's respiratory system during the breathing cycle, will bedetectable for some distance down the gas supply lines from the heads 72of the nasal cannula 128. It must also be noted, however, that themagnitude of pressure variation in the gas supply lines and the degreeto which it accurately reflects the conditions within the respiratorypassages of the patient will notably decrease with an increasingdetection distance from the heads 72 which, in turn, effects the designand the implementation of the flow regulating mechanism 154

In a first implementation, the flow regulating mechanism 154 may be anin-line flow regulating mechanism that will typically include an in-lineflow regulating valve 156V and a flow regulating sensor 156S. Flowregulating valve 156V regulates the flow of gas to the nasal cannulaassembly 126 during the breathing cycle by presenting a gas flowresistance that varies proportionally to the gas flow resistance of thepatient's respiratory system, that is, so that the volume of gas flowingto the nasal cannula 128 is inversely proportional to the flowresistance of the patient's system. The inverse relationship between gasflow volume to the nasal cannula 128 and the flow resistance of thepatient's system there results in a relatively constant pressure in thepatient's system at the discharge/upper end of heads 72 of the nasalcannula 128.

In the in-line regulation method, the varying resistance presented bythe patient's respiratory passages during the breathing cycle, and theresulting pressure fluctuations, are effectively moved “upstream” fromthe nasal cannula 128 and the in-line flow regulating valve 156V, thatis, in the direction of supply line 134 and the source 140. Conversely,the volume of gas flow from in-line flow regulating valve 156V to thenasal cannula 128, that is, “downstream” of the flow regulating valve156V, is varied inversely to the varying flow resistance presented bythe patient's respiratory passages, so that there is an effectivelyconstant gas pressure at the heads 72 of the nasal cannula 128.

The in-line flow regulating valve 156V may be implemented, for example,as a spool valve or some other conventional pressure reduction orregulating valve, and the sensor 156S may be, for example, as a pressuresensor located between the connector 136 and the nasal cannula 128 orthe head 72, and is preferably located at or sufficiently close to thehead 72.

In an alternate implementation of the in-line flow regulating mechanism154, the function of the sensor 156S may be performed by a gas flowsensor 152, as described herein above, that measures volume of gas flowrather than gas pressure. According to this implementation, the sensorelement 152S would be placed, for example, in the head 72 of the nasalcannula 128 to sense the volume of gas flowing through the nasal cannula128 and into the patient's respiratory system. The flow regulatingmechanism 154 will then respond to the gas flow measurements byadjusting the flow resistance of regulating valve 156V, that is, thevolume of gas flowing to nasal cannula 128, to maintain a predeterminelevel of positive gas flow into the nasal cannula 128 throughout thevariations in the respiratory system internal pressure due to inhalationand exhalation. The respiratory system internal pressure will therebyvary throughout the breathing cycle, but will continuously be positivewith respect to room ambient pressure.

In a further alternative implementation, the valve of the flowregulating mechanism 154 may be a flow venting valve 158V that, ratherthan presenting a variable resistance in the flow of gas to the nasalcannula 128, controls the flow of gas supplied to the nasal cannula 128and a portion of which is to be vented as excess gas flow into thesurrounding environment. As indicated, a flow venting valve 158V has aregulated passage 158P connected from the gas supply line 134 or from apoint along the gas flow path between the connector 136 and the nasalcannula 128 which vents to room ambient pressure. The flow volume of thegas through the venting valve 158V, that is, the volume of gas allowedto vent through venting valve 158V is again controlled by a pressuresensor or a gas flow sensor element 152S, in the manner discussed above.

Since certain changes may be made in the above described respiratorytherapy system without departing from the spirit and scope of theinvention herein involved, it is intended that all of the subject matterof the above description or shown in the accompanying drawings shall beinterpreted merely as examples illustrating the inventive concept hereinand shall not be construed as limiting the invention.

The invention claimed is:
 1. A nasal cannula for supplying a respiratorygas to a patient, the nasal cannula comprising: a pair of supply lineswhich each have a head at one end thereof with a discharge openingtherein for discharging a respiratory gas, and the opposite end of eachof the pair of supply lines being connectable to a respiratory gassource, the respiratory gas being supplied at a flow rate of at leastabout 120 liters per minute and at a pressure of between 4 and 20 cm ofH₂O; a central bridge member, having a sufficiently short axial length,configured to span substantially no more than a width of a philtrum of apatient and being located adjacent the heads for integrally connectingto the supply lines to one another; and each head being sized to besnugly received and retained within one of the nasal cavities of thepatient while forming a sufficient leakage passage, between a portion ofinwardly facing nasal cavity skin of a patient and a portion of anexterior surface of the head, to facilitate exhausting of excessrespiratory gas supplied to the patient through the leakage passage;wherein the central bridge member defines an internal flow passagetherein which provides an interconnecting gas flow path between whichgenerally operates to equalize the flow of gas from the pair of supplylines to the pair of heads and provides alternate flow in the event thatone of the heads becomes partially or completely obstructed orrestricted during use; and the nasal cannula forming an open system suchthat when the respiratory gas is introduced into the nostrils of thepatient's nose, a portion of the respiratory gas, along with a portionof the exhaled gases from the patient, being allowed to leak out throughthe leakage passage via a nostril/head interface.
 2. The nasal cannulaaccording to claim 1, wherein each gas supply line, once attached to apatient in use, upon exiting the nasal cavities of the patient generallyfollows along a cheek of the patient and passes below a chin and near amid-line of a face of the patient; a pair of adjustable straps areattached to the gas supply line and around a head of the patient tofacilitate retention of the nasal cannula to the head of the patient; afirst adjustable strap is attached to a first gas supply line and isadapted to pass from the first gas supply line, above a first ear of thepatient, around a head of the patient, under a second ear of the patientand attach again to a second gas supply line; and a second adjustablestrap is attached to the second gas supply line and is adapted to passfrom the second gas supply line, above the second ear of the patient,around a head of the patient, under the first ear of the patient andattach again to the second gas supply line.
 3. The nasal cannulaaccording to claim 1, wherein an element is located within the gassupply line, along a gas flow path, and the element is coupled to acontroller which controls flow of power to the element for heating thegas flowing through the gas supply line and measuring a temperature ofthe gas flowing through the gas supply line.
 4. The nasal cannulaaccording to claim 1, wherein the gas supply lines each include a spiralreinforcing member which assists with reinforcing a side wall of the gassupply lines.
 5. The nasal cannula according to claim 1, wherein anexterior surface of the head has a plurality elongate troughs formedtherein for partially defining a plurality of leakage passages thereinto facilitate exhausting of any excess respiratory gas and inhalation ofany room air required by the patient.
 6. The nasal cannula according toclaim 5, wherein the exterior surface of the head has between six andeight elongate troughs formed therein which are equally spaced about acircumference of the head, and each of the elongate troughs partiallydefines one of the leakage passages in the head to facilitate exhaustingof any excess respiratory gas and inhalation of any room air required bythe patient.
 7. The nasal cannula according to claim 5, wherein each ofthe plurality elongate troughs is formed by a pair of adjacent planarside surfaces which diverge away from a common elongate valley toward apair of spaced apart but adjacent elongate ridges to partially defineone of the plurality of leakage passages.
 8. The nasal cannula accordingto claim 5, wherein each one of the leakage passages has a crosssectional open area of between about 0.002 square inches (0.013 cm²) and0.0055 square inches (0.035 cm²); and each head has a maximum widthdimension of between about 0.345 of an inch (0.88 cm) about 0.70 of aninch (1.8 cm) and a length of between about 0.30 of an inch (0.76 cm)and about 0.60 of an inch (1.5 cm).
 9. The nasal cannula according toclaim 1, wherein the central bridge member aligns the pair of supplylines parallel to one another to facilitate insertion of the heads,carried by the pair of supply lines, within the nostrils of the patient.10. The nasal cannula according to claim 1, wherein the nasal cannula ismanufactured from a flexible material; and a second end of each of thesupply lines bends away from one another and is curved so as to conformgenerally with a curvature of a face of a patient.
 11. The nasal cannulaaccording to claim 10, wherein the second end of each of the supplylines is coupled to an auxiliary respiratory gas supply line, at leastthe second end of each of the supply lines has a sufficient stiffness soas to urge the attached auxiliary respiratory gas supply line, coupledthereto, to pass beneath a patient's cheekbone area when the nasalcannula is donned by a patient.
 12. A nasal cannula assembly forsupplying a respiratory gas to a patient, the nasal cannula assemblycomprising: a pair of supply lines which each have a head at one endthereof with a discharge opening therein for discharging a respiratorygas, and the opposite end of each of the pair of supply lines beingconnected to an auxiliary respiratory gas supply line, and a remote endof each of the auxiliary respiratory gas supply line is connected with arespiratory gas source for supplying a respiratory gas to a patient, therespiratory gas being supplied at a flow rate of at least about 120liters per minute and at a pressure of between 4 and 20 cm of H₂O; acentral bridge member being located adjacent the heads for integrallyconnecting to the supply lines to one another; and each head being sizedto be snugly received and retained within one of the nasal cavities ofthe patient while forming a sufficient leakage passage, between aportion of inwardly facing nasal cavity skin of a patient and a portionof an exterior surface of the head, to facilitate exhausting of excessrespiratory gas supplied to the patient through the leakage passage;wherein the central bridge member defines an internal flow passagetherein which provides an interconnecting gas flow path between whichgenerally operates to equalize the flow of gas from the pair of supplylines to the pair of heads and provides alternate flow in the event thatone of the heads becomes partially or completely obstructed orrestricted during use; and the nasal cannula forming an open system suchthat when the respiratory gas is introduced into the nostrils of thepatient's nose, a portion of the respiratory gas, along with a portionof the exhaled gases from the patient, being allowed to leak out throughthe leakage passage via a nostril/head interface.
 13. The nasal cannulaaccording to claim 12, wherein each gas supply line is adapted attach toa patient and each gas supply line, once attached to a patient in use,upon exiting the nasal cavities of the patient generally follows along acheek of the patient and passes below a chin and near a mid-line of aface of the patient; a pair of adjustable straps are attached to the gassupply line and around a head of the patient to facilitate retention ofthe nasal cannula to the head of the patient; a first adjustable strapis attached to a first gas supply line and is adapted to pass from thefirst gas supply line, above a first ear of the patient, around a headof the patient, under a second ear of the patient and attach again to asecond gas supply line; a second adjustable strap is attached to thesecond gas supply line and is adapted to pass from the second gas supplyline, above the second ear of the patient, around a head of the patient,under the first ear of the patient and attach again to the second gassupply line and the pair of adjustable straps are adapted to cross oneanother at only one location behind the head of the patient.
 14. Thenasal cannula according to claim 12, wherein an element is locatedwithin the gas supply line, along a gas flow path, and the element iscoupled to a controller which controls flow of power to the element forheating the gas flowing through the gas supply line and measuring atemperature of the gas flowing through the gas supply line.
 15. Thenasal cannula assembly according to claim 14, wherein the nasal cannulais manufactured from a flexible material; and a second end of each ofthe supply lines bends away from one another and is curved so as toconform generally with a curvature of a face of a patient.
 16. The nasalcannula assembly according to claim 15, wherein the second end of eachof the supply lines is coupled to an auxiliary respiratory gas supplyline, at least the second end of each of the supply lines has asufficient stiffness so as to urge the attached auxiliary respiratorygas supply line, coupled thereto, to pass beneath a patient's cheekbonearea when the nasal cannula is donned by a patient.
 17. The nasalcannula according to claim 12, wherein the gas supply lines each includea spiral reinforcing member which assists with reinforcing a side wallof the gas supply lines.
 18. The nasal cannula assembly according toclaim 12, wherein an exterior surface of the head has a pluralityelongate troughs formed therein for partially defining a plurality ofleakage passages therein to facilitate exhausting of any excessrespiratory gas and inhalation of any room air required by the patient;and the exterior surface of the head has between six and eight elongatetroughs formed therein which are equally spaced about a circumference ofthe head, and each of the elongate troughs partially defines one of theleakage passages in the head to facilitate exhausting of any excessrespiratory gas and inhalation of any room air required by the patient.19. The nasal cannula assembly according to claim 18, wherein each ofthe plurality elongate troughs is formed by a pair of adjacent planarside surfaces which diverge away from a common elongate valley toward apair of spaced apart but adjacent elongate ridges to partially defineone of the plurality of leakage passages.
 20. The nasal cannula assemblyaccording to claim 18, wherein each one of the leakage passages has across sectional open area of between about 0.002 square inches (0.013cm²) and 0.0055 square inches (0.035 cm²).
 21. The nasal cannulaassembly according to claim 18, wherein each head has a maximum widthdimension of between about 0.345 of an inch (0.88 cm) about 0.70 of aninch (1.8 cm) and a length of between about 0.30 of an inch (0.76 cm)and about 0.60 of an inch (1.5 cm).
 22. A respiratory therapy system forsupplying a respiratory gas to a patient via a nasal cannula, therespiratory therapy system comprising: a source of respiratory gas forsupplying a respiratory gas to a patient, and the source of respiratorygas supplying the gas at a flow rate of at least about 120 liters perminute and at a pressure of between 4 and 20 cm of H₂O; a nasal cannulaconnected to the source of respiratory gas for receiving the respiratorygas and supplying the respiratory gas to nostrils of a patient; thenasal cannula comprising: a pair of supply lines which each have a headat one end thereof with a discharge opening therein for discharging arespiratory gas, and the opposite end of each of the pair of supplylines being connected to an auxiliary respiratory gas supply line, and aremote end of each of the auxiliary respiratory gas supply line isconnected with the source of respiratory gas for supplying a respiratorygas to a patient; a central bridge member being located adjacent theheads for integrally connecting to the supply lines to one another; andeach head being sized to be snugly received and retained within one ofthe nasal cavities of the patient while forming a sufficient leakagepassage, between a portion of inwardly facing nasal cavity skin of apatient and a portion of an exterior surface of the head, to facilitateexhausting of excess respiratory gas supplied to the patient through theleakage passage; wherein the central bridge member defines an internalflow passage therein which provides an interconnecting gas flow pathbetween which generally operates to equalize the flow of gas from thepair of supply lines to the pair of heads and provides alternate flow inthe event that one of the heads becomes partially or completelyobstructed or restricted during use; the nasal cannula forming an opensystem such that when the respiratory gas is introduced into thenostrils of the patient's nose, a portion of the respiratory gas, alongwith a portion of the exhaled gases from the patient, being allowed toleak out through the leakage passage via a nostril/head interface; eachgas supply line is adapted to attach to a patient such that when in use,upon exiting the nasal cavities of the patient each gas supply linegenerally follows along a cheek of the patient and passes below a chinand near a mid-line of a face of the patient; and a pair of adjustablestraps are attached to the gas supply lines and are adapted to wraparound a head of the patient to facilitate retention of the nasalcannula to the head of the patient.
 23. The respiratory therapy systemaccording to claim 22, wherein the respiratory therapy system furtherincludes a heater for heating the respiratory gas to a desiredtemperature prior to delivering the respiratory gas to the patient; andthe respiratory therapy system further includes a humidifier forsupplying humidity to the respiratory gas prior to delivering therespiratory gas to the patient.
 24. The respiratory therapy systemaccording to claim 23, wherein a humidity sensor and a temperaturesensor are coupled to a controller to provide inputs concerning thehumidity and the temperature of the respiratory gas, and the controllercontrols operation of the humidifier and the heater to control thetemperature and the humidity of the respiratory gas prior to delivery tothe patient.
 25. The respiratory therapy system according to claim 24,wherein the respiratory gas system provide the respiratory gas at arelative humidity of between about 70 percent and 100 percent and atemperature of between about 80° F. (26.6° C.) and about 90° F. (32.2°C.).
 26. The respiratory therapy system according to claim 22, whereinthe respiratory therapy system provides a variable flow of respiratorygas, during operation of the respiratory therapy system, of betweenabout 20 and 120 liters per minute.
 27. The respiratory therapy systemaccording to claim 15, wherein the respiratory gas system furtherincludes a respiratory gas metering device to facilitate conservation ofuse of the respiratory gas during operation of the respiratory gassystem.
 28. The respiratory therapy system according to claim 22,wherein the respiratory gas supply lines and the nasal cannula each havegradual bends, transitions, expansion and contraction therealong so thatthe respiratory gas, as the respiratory gas flows from the source ofrespiratory gas to the nasal cannula, minimizes generation of noise. 29.The respiratory therapy system according to claim 22, wherein therespiratory therapy system further includes a heater for heating therespiratory gas to a desired temperature prior to delivering therespiratory gas to the patient.
 30. The respiratory therapy systemaccording to claim 22, wherein the respiratory therapy system furtherincludes a humidifier for supplying humidity to the respiratory gasprior to delivering the respiratory gas to the patient.
 31. A method oftreating a patient with sleep disorder with a respiratory gas, themethod comprising the steps of: inserting prongs of a nasal cannulawithin respective nostrils of the patient; supplying a respiratory gasto the nasal cannula at a constant flow rate sufficient to form a backpressure within the breathing passageways of the patient, at least whenthe patient is exhaling, the respiratory gas being supplied at a flowrate of at least about 120 liters per minute and at a pressure ofbetween 4 and 20 cm of H₂O; forming the nasal cannula as an open systemsuch that when the respiratory gas is introduced into the nostrils ofthe patient's nose, a portion of the respiratory gas, along with aportion of the exhaled gases from the patient, is permitted to leak;allowing, at least during exhalation, a portion of the suppliedrespiratory gas to leak from the nostril between the prongs of the nasalcannula and inwardly facing skin of the nostril; attaching each gassupply line to the patient such that, upon exiting the nasal cavities ofthe patient each gas supply line generally follows along a cheek of thepatient and passes below a chin and near a mid-line of a face of thepatient; and attaching a pair of adjustable straps to the gas supplylines and wrapping each of the pair of adjustable straps around a headof the patient to facilitate retention of the nasal cannula to the headof the patient.
 32. The method of treating the patient with sleepdisorder according to claim 31, further comprising the steps of usingoxygen as the respiratory gas and supplying the oxygen a flow rate ofbetween about 20 and 120 liters per minute.
 33. The method of treatingthe patient with sleep disorder according to claim 31, furthercomprising the steps of forming each prong of the nasal cannula with ahead at one end thereof having a discharge opening therein fordischarging the respiratory gas, and the opposite end of each prong iscoupled to a supply line which is connected to a respiratory gas source;and each head is sized to be snugly received and retained within one ofthe nasal cavities of the patient while forming a sufficient leakagepassage, between a portion of inwardly facing nasal cavity skin of apatient and a portion of an exterior surface of the head, to facilitateexhausting of any excess respiratory gas supplied to the patient throughthe leakage passage and also facilitate inhalation of any room airrequired in excess of the respiratory gas to be supplied to the patient.34. The method of treating the patient with sleep disorder according toclaim 31, further comprising the step of heating the respiratory gas toa desired temperature prior to delivering the respiratory gas to thepatient.
 35. The method of treating the patient with sleep disorderaccording to claim 31, further comprising the step humidifying therespiratory gas prior to delivering the respiratory gas to the patient.36. The method of treating the patient with sleep disorder according toclaim 31, further comprising the steps of: heating the respiratory gasto a desired temperature; and humidifying the respiratory gas to desiredhumidity prior to delivering the respiratory gas to the patient.
 37. Themethod of treating the patient with sleep disorder according to claim31, further comprising the step of interrupting the constant flow rateof the respiratory gas, with a metering device, to facilitateconservation of the respiratory gas during treatment of the patient withsleep disorder.